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NE Handbook series 2011Microcontrollers


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Guidelines for Selecting a Microcontrollerwith Required Functionsand Performance

Examine Product Specications

Control System

Select CPU and Peripheral Functions

According to Usage

Signal Processing System

Ensure Performance Meeting Requirement

Specications

Combined System

Examine Communication Standard between

Microcontroller and Other Devices

Examine Restricting Conditions

[ Column ]

The World's First Microprocessor

Born of the Calculator Wars "The 4004"

Microcontroller GlossaryCPU

Multi-Core

Embedded Flash Memory

Real-Time OS

Integrated Development Environment

DSC

Instruction Set Architecture

Analog Circuit

Serial Communication Interface

Genealogy of MicrocontrollersARM

Microcontroller-Dedicated Cores Derived

from General-Purpose Processor Cores

MIPS

Began as Processors for Workstations,Now Primarily Used for Embedded Applications

Renesas

Multiple Product Lines with Origins

in Three Companies,

Likely to be Integrated in One Line

Freescale

World's First Developer of

One-Chip Microcontroller Gains Edge

in Applications for Automobiles

and Communication Devices

NEHandbook2011

M

icrocontrollers


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2 3

Mark ZackVice President of Semiconductor ProductDigi-Key Corporation

PR

Fully FeaturedMicrocontrollers SeeStrong Market Demand

Q What is the worldwide market trend for micro-

controllers in 2011?

Zack We expect to see continued expansion as micro-

controllers become more pervasive in our everyday lives.

Rapid advancements in smart medical devices, smart grids

and smart automobiles are driving growth. Semico Re-

search Corp. reports that the microcontroller industry will

grow by more than 13% in 2011.

Handling a large product portfolio

Q How many microcontroller vendors and items do

you handle? What are some of your microcontroller

vendor business partners?

Zack Today, we carry microcontrollers from roughly 20

manufacturers and sell more than 29,000 individual de-

vices.

Digi-Keys wide microcontroller portfolio includes devices

from Analog Devices, Atmel, Cirrus, Cypress, Energy Mi-

cro, Freescale, Fujitsu, Infineon, Maxim, Microchip, NXP,

Parallax, OKI Semiconductor/ROHM, Renesas, Silicon

Laboratories, ST Microelectronics, TI, Toshiba, and Zilog.

Comprehensive platforms support customers

Q Do you also handle software development kits, refer-

ence boards, and peripherals for microcontrollers?

With cutting-edge technologies like smart grids and

automobiles pushing demand for new functions such

as higher clock speeds, wider bus paths, and extended

peripherals on-chip, microcontrollers are becoming

more powerful and feature-laden. They are expected to

see strong market growth in 2011. We sat down with

Mark Zack,Vice President of Semiconductor Product,

Digi-Key Corporation, to discuss market and technol-

ogy trends, and to learn how the company efficiently

handles so many products to meet worldwide demand.


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Digi-Key CorporationTel1-800-344-4539Fax218-681-3380USURLhttp://www.digikey.com/

PR

Zack Digi-Key has one of the most complete oerings of

design platforms for the engineering community. We sup-

port manufacturers design tools and platforms along with

the vast majority of qualied third-party support compa-

nies.

The expansion of these third parties has been a big push

for Digi-Key in the recent past. We have added numerous

partners that support controller manufacturers with mid-

dleware, compilers, integrated development environments,

development platforms, single-board computers, program-

mers, emulators, and more.

Q What trends are customers looking for in micro-

controllers now?

Zack Customers power considerations have pushed

manufacturers to produce devices that have low sleep cur-

rent, low active current, and fast wake-up times. As elec-

tronic devices become more interactive, microcontroller

technology will have to stay a step ahead of these devices.

With this in mind, designers will continue to require con-

trollers with higher clock speeds, wider bus paths, and ex-

tended peripherals on-chip to support these requirements.

Targeting fast shipments

Q How do you build the procurement, inventory, and

speedy delivery system for users? How many items

are stored in your warehouse? Do you buy micro-

controllers directly from original makers?

Zack We target a 95% in-stock rate for all products we

carry. This allows us to ship products the same day from

our facility in the U.S. and deliver them worldwide in 2 4

days.

Our product distribution center is organized in a way that

allows us to process and package orders quickly and ac-

curately. We are able to process an average order and

have the product picked, packed, and placed on a truck

for shipment in approximately 15 minutes.

We have some 600,000 part numbers on hand for imme-

diate shipment. We are an authorized, franchise distribu-

tor for every supplier on our line card. We only purchase

products directly from the manufacturers.

Q Please describe your after-sale and technical sup-

port for microcontrollers.

Zack Technical support is provided for all products that

Digi-Key sells. Support levels range from basic requests,

such as aiding in the selection of devices for specic re-

quirements, to assisting with debugging and laying out

projects.

Our technical support department is staffed 24 hours a

day and is available via phone, e-mail, and web-chat inter-

action.


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6 7

Guidelines for Selecting a Microcontroller

Control system

Combined system

Signal processing

system

Product

specifications

CPU

Input/output (I/O) port

A/D converter

Timer (counter)

Interrupt

Bus interface

Arithmetic circuit

Middleware

Communications

between multiple processors

Delivery time, costs

Development assets

Development environment

Restricting

conditions

Fig. 1Points to consider in selecting a microcontroller

General points are given above.

Guidelines for Selecting a Microcontrollerwith Required Functionsand Performance

There is a wide variety of microcontrollers available and even if

you have decided on which series to use, you still have plenty

of choices. Engineers must have their own criteria in order

to make the right selection. This article discusses the general

considerations and some tips to keep in mind when selecting a

microcontroller, serving as a basis for setting your own criteria.

Today, microcontrollers are incorporated in many devices

used in our daily lives. For example, oce automation equip-

ment such as copiers and factory automation equipment inplants are equipped with one or more microcontrollers. It is

almost dicult to nd a device that does not have one.

On what criteria should an engineer make a choice among

microcontrollers, which are used in various applications?

This article discusses the considerations in selecting a micro-

controller.

When you chose a microcontroller, you must examine the

delivery time, costs, development assets and development

environment, in addition to the product specications (Fig.

1). Here, the delivery time and costs, etc. are referred to

as restricting conditions and the general ways to make a

selection with regard to the product specications and the

restricting conditions will be explained. Microcontrollers are

used for a wide range of applications and there are a lot of

dierent ways to select one. You have to organize your own

opinions beforehand, because the points to be considered

may vary depending on the product you are planning to

develop.

The article also covers the problems frequently faced in

actual development. The article discusses things that are

likely to be overlooked by software engineers who are not

familiar with how electronics operate or electronic engineers

who know little about software, even if they are experienced

in their own elds.


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Points to

consider Specific suggestions and possible problems

Function,

circuit

External ports may runshort when they are

shared.

A resistor may have to be added later on.

An external driver circuit has to be added

if the allowable output current is insufficient.

Number of

external ports

Pullup/

pulldown

Allowable output

current of output port

Input/

output

(I/O)

port

The accuracy may be insufficient due to

unavailability of an external clock.

Consult the timer usage examples and theapplication notes.

Timers may run short when a real-time OS is

adopted.

Time

measurement

Cooperation withperipheral functions

Number of

timers

Timer(counter)

Make sure that the ports will not run short

when they are shared with other functions.

Check the capability to perform edge detection,

level detection, etc., of input signal waveforms.

Check whether the priority level can be set

for reset and other processes.

Number of input ports

for interrupt signals

Interrupt detection

method

Processing

priority setting

Interrupt

The resolution may be decreased due to noise,

signal wiring on the board, power supply, etc.

Check whether the conversion process completes

within the period required for the control process.

The process may not complete in time due to

the time required to switch channels.

Resolution

Conversion time

Number of

channels

A/D

converter

Check that the CPU operation bit rate matches

those of the A/D converter and the timer.

Check the operating frequency.

(Exaggerated specifications lead to increased cost.)

Operation bit

rate

Responsiveness

CPU

Fig. 3Example guidelines for selecting microcontroller for control

systemCPU ROM RAM Clock

A/D

converterTimer

Serial

interface

Input/output

(I/O) port

DMA

controller

Fig. 2Block diagram of microcontroller

A supply voltage detection circuit and application-specific blocks

are also included.

Examine Product Specifcations

A microcontroller acts as the brains to run the system. It

also has various peripheral functions to meet the capability

and performance required for the system (Fig. 2). Therefore,

the microcontroller to be used may vary depending on the

characteristics and specifications of the system. In the fol-

lowing, we divide systems roughly into two categories

control and signal processing systems and provide some

general points to consider in selecting a microcontroller.

Control System

Select CPU and Peripheral Functions

According to Usage

An electronic hot water dispenser, a home appliance, can

be given as an example of a control system. It boils water and

keeps it hot by cleverly controlling temperature and water

level sensors and an electronic heater. When the user pushes

the button, the hot water dispenser pours hot water by acti-

vating a pump. In short, the microcontroller in an electronic

hot water dispenser cooperates with the temperature and

water level sensors to control electronic components such as

the heater and pump.

When selecting a control system microcontroller used for

such applications, it is common to consider the performance

and operating frequency of the central processing unit (CPU)

and the peripheral functions (Fig. 3).


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The following discusses the criteria and tips to keep in

mind when selecting a microcontroller with such peripheral

functions.

[ CPU ]

Watch out for Exaggerated Specications

A microcontroller intended for control applications gener-

ally employs a CPU with sucient performance to properly

control the peripheral functions used. However, when mak-

ing a choice, you need to check that the operation bit rate

matches the data length of the peripheral functions handled

by the microcontroller (e.g., the bit rate of the analog-to-

digital (A/D) converter or a timer).

In addition, make sure that you select a microcontroller

equipped with a CPU with an operating frequency that cansufficiently ensure the responsiveness (real-time property)

required for the product. Note, however, that a higher op-

erating frequency can increase the power consumption

and pose a greater risk of extra costs required to prevent

unwanted radiation. To avoid exaggerated specifications, it

is important to balance the specications with the required

performance.

[ Input/output port ]

Pay Attention to Number of External Ports

and Pullup Functionality

The input/output (I/O) port is one of the typical functions

of microcontrollers for use in control systems. For example,

the I/O ports are used for operation switch on/o detection,

light-emitting diode (LED) indicator on/o control and infor-

mation exchange with the other devices that cooperate with

the microcontroller to constitute the system.

Regarding the I/O ports, you have to pay attention to the

number of input ports, output ports and input/output ports

provided, the number of external ports that can be used

simultaneously and the availability of pullup (or pulldown)

functionality. In addition, you need to be careful about the

allowable output current of the output ports.

The number of external ports should be determined ac-

cording to the number of operation switches to be detected

and the number of LEDs to be controlled. If the number

of ports is insufficient, you have to examine whether the

problem can be addressed by adding external logic circuits.

Then, select a product that can secure at least the minimum

required number of ports. In many cases, the external ports

are also used as ports for other functions of microcontroller.

You need to be aware of this because you will often have

trouble in allocating the ports as you continue with the cir-

cuit design.

Pullup or pulldown functionality is a necessary feature for

I/O ports. In the case of operation switch on/off detection,

the port has to be xed either to the H or L level when the

switch circuit is open. If an input port of a microcontroller

is not provided with pullup or pulldown functionality, an ex-

ternal resistor is required. You should be aware of this when

you design the circuit, otherwise you may have to provide

an additional resistor on a high-density printed circuit board

(PCB) later on and this can cause a lot of trouble.

The allowable output current of the external port should

be determined according to the value of current that must

be supplied to the circuit connected. In controlling an LED,

for example, a current of several milliamperes needs to be

supplied. If this exceeds the allowable output current of the

output port of a microcontroller, you need an external drive

circuit.


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[ A/D converter ]

Resolution and Number of Channels may Dier from

Specication Sheet

In control systems, an A/D converter is familiar as a func-

tion to fetch electric signals into the microcontroller from

a sensor and so on. In the case of an electronic hot water

dispenser, for example, electric signals from a temperature

sensor such as a thermistor are A/D converted and then

fetched into the microcontroller via the input port to control

the temperature, while the heater and other components are

controlled by using the output port.

In respect to the A/D converter, the main points to be

considered are the resolution (bit count) and the conver-

sion time. The resolution should be determined so that it is

neither lower nor higher than the accuracy of the electronic

signals (the level of noise contained in the signals, etc.)output by the sensor and that it adequately meets the data

accuracy (granularity, etc.) required for control. The con-

version time should be determined so that the conversion

process completes within the period required for the control

process.

If you decide to use the A/D conversion functionality in-

corporated in the microcontroller, there are some things

to keep in mind about the resolution of A/D conversion. To

tell the truth, you cannot fully trust the resolution indicated

in the microcontroller specification sheet. A/D converters

are basically analog circuits and thus the performance you

can get out from them may vary depending on the distance

to the sensor, the mounting condition on the PCB and the

state of power supply to the system. When high accuracy is

required for the A/D conversion results, it may be better to

give up using the A/D conversion functionality incorporated

in the microcontroller and separately adopt an external A/D

conversion device.

Furthermore, you have to be careful about the number of

channels that can simultaneously perform A/D conversion

if electric signals from multiple sensors have to be A/D con-

verted. If the number of input ports used for A/D conversion

and the number of built-in A/D converters do not match,

then A/D conversion has to be performed by switching over

the channels. You need to pay attention to the time required

to switch the channels, as well as the method and required

time for the CPU to read the converted data. Sometimes

you may realize later on that A/D conversion cannot be per-

formed within the required period. Select a microcontroller

with the right A/D conversion functionality after you have

fully understood the accuracy of A/D conversion required for

the system.

[ Timer ]

Check Accuracy and Number of Timers

A timer is also an essential function for control systems.

In regard to timer functionality, it is important to consider

not only whether it can properly measure the time, but also

whether it can make multiple timers cooperate with one an-

other or make timers cooperate with other peripheral func-

tions. It is also important to consider the number of timers.

As far as time measurement is concerned, you have to pay

attention to the type and accuracy of the clock that drives

the timer. When choosing a timer, you have to take into ac-

count whether the clock used to drive the microcontroller

(or its frequency-divided clock) or other clocks supplied

externally can be selected as the clock to drive the timer,

as well as the range of clock frequencies countable by the

timer, depending on the type of time to be measured. When

the rotational speed of a motor, etc., is detected by externally

supplying the pulse output of a rotation sensor, for example,

you need to check whether the pulse generation period can

be counted properly.


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As for cooperation with peripheral functions, you should

pay attention to whether the external port can be controlled

when the specified count value is reached, whether the

counter value can be automatically obtained when changes

in the external port are detected and whether multiple tim-

ers can be operated in conjunction with one another. When

a three-phase motor is inverter controlled, for example,

pulse width modulation (PWM) waveforms in three phases

should be output. For this purpose, there is a microcontroller

designed to easily output the PWM waveforms by enabling

collaboration between multiple timers and I/O ports. When

a microcontroller is designed for a particular application as

mentioned above, timer usage examples may be given in the

specication sheet or a separate document may be provided

as application notes. It is important to effectively use such

documentation in selecting a microcontroller.

You need to be very careful about the number of timers.If the number is insucient, you may have a hard time, for

example, adding an extra piece of external hardware during

development. This applies to the case when, for example, the

circuit design is initially developed by a team of hardware

engineers alone and then the adoption of a real-time operat-

ing system (OS) is decided after a software engineer joins

the team in the course of development. A real-time OS gener-

ally takes up one timer function in the microcontroller as a

system timer. Thus, an extra timer is required in excess of

the number of timers necessary for the originally intended

control.

[ Interrupt ]

Determine the Number of Input Ports

and Detection Method

Interrupts are extremely important functions to detect

various phenomena (events) that occur in and outside the

microcontroller. There are a number of causes of interrupts,

e.g., the detection of an operation button being pushed, a

communication request notication from other devices that

work in conjunction with the microcontroller and the recep-

tion of a notification about the completion of conversion

process carried out by a built-in A/D converter. In particular,

with regard to events that occur outside the microcontroller,

you have to pay attention to the number of ports to which in-

terrupt signals are input and whether the detection method

can be selected.

The number of input ports for interrupt signals should be

determined based on whether the number of causes of inter-

rupts extracted during the circuit design is met. You need to

make sure that you have a sufficient number of ports that

can actually be used, because these ports are often shared

with other functions as in the case of I/O ports. Regarding

the interrupt detection method, you need to check whether

the interrupts can be detected not only at the rising ortrailing edge of an input signal, but also by other detection

methods (such as level detection) that are suitable for the

characteristics of the causes of interrupts.

In general, interrupts are regarded as one of the exception

handling processes. You need to consider how to specically

set the processing priority among other exception handling

processes (e.g., reset or error detection, system call, etc.) and

whether you can mask (temporarily suspend) other causes of

interrupts.

Signal Processing System

Ensure Performance Meeting

Requirement Specications

When image and audio signals are digitalized for use, the

signals are processed in a number of dierent ways in ac-

cordance with the application. When playing back music on


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Circuit and points

to consider

Specific suggestions and possible

problems

Coprocessor/

built-in DSP

Check whether the coprocessor or the built-in

DSP can perform the desired operations.

Built-in RAMSelect a capacity that can store the

operation programs.

Bus transfer rateCheck whether the bus can properly

transfer data.

Cooperation with

peripheral functions

Check the bus connection specifications between

the CPU and the coprocessor or the built-in DSP.

Bus connection

specifications

Check the DMA mechanism and the

arbitration specifications.

Bus architectureCheck, for example, whether the

Harvard architecture is adopted.

Microcontroller

evaluation kit

Check the operation and measure the

performance.

Function,

circuit

CPUPay attention to the power consumption and

unwanted radiation, as well as the performance.

Arithmetic

circuit

Bus

interface

Support systemCheck whether a support system is provided

by the manufacturers of the microcontroller, etc.Middleware

Fig. 4Example guidelines for selecting a microcontroller for signal

processing system

a portable music player, for example, the microcontroller

used in the system reads audio data that has been com-

pressed such as the MPEG-1 audio layer III (MP3) from the

NAND flash memory, etc., incorporated in the system and

decodes the data into music signals.

This is a typical application of signal processing systems.

In particular, the items listed in Fig. 4 should be taken into

consideration when selecting a microcomputer used for

such applications. Here, we will discuss the criteria and tips

when making choices regarding these items.

[ Arithmetic Circuit ]

Prepare Solutions for Operations that

Cannot be Processed by CPU

If the arithmetic performance of the microcontroller used

for signal processing is insufficient, you cannot develop a

satisfactory device. Thus, the arithmetic performance must

be properly ensured. As far as the arithmetic performance

is concerned, the existence or nonexistence of a copro-

cessor, built-in digital signal processor (DSP) and built-in

random access memory (RAM) in addition to the CPU is

important.

With respect to the processing speed of the CPU, which

is the main function of a microcontroller, you have to rst

roughly estimate the number of signal processing steps

required per unit time. Then, make sure whether the CPU

can properly handle the processing necessary for data

input/output and the user interface, etc. As in the case of

control-oriented microcontrollers, you have to give special

consideration to the power consumption and unwanted

radiation if a high operation clock is required.

You also need to check whether a coprocessor or DSP

capable of performing multiply-and-accumulate operations,

etc., is included in the microcontroller. For example, in or-

der to add sound eects to audio signals, arithmetic opera-

tions must be performed for an infinite impulse response

(IIR) or nite impulse response (FIR) lter. However, these

operations may not be carried out by the simple combina-

tion of CPU instructions or they may require an enormous

number of processing steps. Moreover, when performing

integer or fixed-point arithmetic, the accuracy required

for the system may not be ensured. Thus, the capability

to perform floating-point arithmetic with a small number

of processing steps significantly affects the arithmetic

performance. Needless to say, you can use multiple micro-

controllers or separately provide a dedicated DSP if the

required arithmetic performance cannot be ensured with a

single microcontroller.

Built-in RAM is indispensable to eectively perform arith-

metic operations because it can be accessed from the CPU,


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coprocessor or DSP without causing unnecessary overhead.

Generally, signals are processed by periodically repeating

one arithmetic program. If the program is entirely deployed

in built-in RAM, the execution speed can be expected to

increase signicantly. Pay attention to the number of cycles

required to access the built-in RAM and its size when select-

ing a microcontroller used for the applications mentioned

above.

[ Bus Interface ]

Prevent Congestion of Data

It is absolutely necessary to consider whether the data can

be properly supplied and transmitted in and outside a micro-

controller. In other words, you also need to pay attention to

the bus interface. In this case, check the data transfer rate

of the bus, the capability to cooperate with peripheral func-tions such as a direct memory access (DMA) mechanism and

whether the Harvard architecture is adopted in which the

instruction and data buses are separated.

A microcontroller operates by sequentially processing

instructions for the CPU one at a time. The series of instruc-

tions has to be read via the bus from the memory that stores

the programs. Data transferred by DMA is also read via the

bus from memory or a peripheral function block and the

processed data is then written. The bus is a path for these in-

structions and data and the bus interface serves to eciently

pass them via the bus. Therefore, the performance of the bus

interface, which arbitrates the operations of the functions, is

extremely important in order for the CPU, coprocessor, built-

in DSP and DMA mechanism, etc., to share the bus.

When audio data is transferred by DMA from a device that

takes a considerable amount of time for readout, for exam-

ple, if the DMA mechanism occupies the bus during the read-

out, the CPU cannot read the instructions and has to suspend

the signal processing during that time. If the audio output is

interrupted in a piece of audio equipment as a consequence,

it would be a fatal aw for the product.

To avoid such problems, you need to check the microcon-

troller specification sheet for the specifications of the bus

interface so as to fully understand the specications of the

bus connections between the CPU and the coprocessor or

the built-in DSP, as well as between the CPU and the cache

memory or the built-in RAM. You also need to check the bus

conguration (just in case that the instruction and data buses

are separated as mentioned above) and the arbitration speci-

cations with respect to the DMA mechanism. If possible, it

is recommended that you use the evaluation kit of the micro-

controller to perform operational tests such as performance

measurement.

[ Middleware ]

Availability of Desired Middleware Matters

There is no sense in selecting a microcontroller with high

arithmetic performance if you cannot use it eectively. When

decoding an MP3 file on a portable music player, for ex-

ample, you need a program that can carry out the operation.

It would require an enormous amount of time and develop-

ment cost if you had to code the operation program each

time you adopted a dierent microcontroller. Moreover, you

cannot make full use of the arithmetic performance if you do

not eectively use the CPU, coprocessor or DSP. In short, you

cannot develop a practical product unless a program tuned

to fully take advantage of the arithmetic performance of a

microcontroller is readily available.

In such cases, whether middleware equipped with the

functionality required for the product is provided by the

microcontroller manufacturer or a third-party vendor is an

important item to check when selecting a microcontroller.


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Specific suggestions and possible problems

Consider the adoption of a microcontroller with flash

memory.

Check the capacity options of the flash memory.

Check the tools used to write programs and their cost.

Delivery time,

cost

Check the performance of the compiler optimization option

function and the support system.

Select a microcontroller that supports a satisfactory

debugging function.

Development

environment

Make sure that the circuits and software can be reused.

Development

assets Select a microcontroller that will continue to be sold and

developed in the future.

Points to

consider

Fig. 5: Examples of restricting conditions to be considered

Combined System

Examine Communication Standard between

Microcontroller and Other Devices

Relatively large systems carry out signal processing and

control in parallel (or rather this type of system may be more

common). For example, a copier analyzes the duplicate data

read from the original document and controls the paper feed

mechanism and ink jetting function to print, while perform-

ing signal processing for the contrast ratio and color tone

correction, etc. A system equipped with a universal serial bus

(USB) port also performs communication control with the

USB device inserted in the port.

Such systems often require the adoption of multiple micro-

controllers or collaboration with dedicated devices such asDSP because the requirements cannot be met just by using

the functionality of one microcontroller.

The point to consider in such cases is the method of com-

munications between the microcontroller and other devices.

A microcontroller normally has several functions to commu-

nicate with other devices. One of the typical functions is the

serial communication function. For example, a bidirectional

asynchronous communication circuit called a universal asyn-

chronous receiver-transmitter (UART), which can be found in

personal computers, etc., or a clock synchronization commu-

nication circuit called a serial peripheral interface (SPI) may

be used.

Neither method can be used if the devices on both sides of

the serial communication use dierent communication stan-

dards. When selecting a microcontroller in such a case, you

need to make sure that the type and the number of channels

of the adopted serial interface meet the specifications re-

quired for the system.

Examine Restricting Conditions

When configuring a system, you have to select the mi-

crocontroller and other components while taking into ac-

count various restricting conditions. In the following, let us

consider the criteria in selecting a microcontroller from the

aspects of delivery time, cost and the utilization of develop-

ment assets (Fig. 5). Since this involves a wide range of con-

siderations, we mainly focus on flash microcontrollers and

middleware, which are commonly used these days.

[ Delivery time, Cost ]

Microcontrollers with Flash Memory

Become Potential Product

You have to prepare programs in order for a microcon-

troller to operate according to the intended specifications.


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Programs are usually stored in memory that cannot be modi-

ed called read only memory (ROM). Ideally, when the prod-

uct specifications are decided, the program specifications

are also determined and programs once created would never

have to be changed. Before being incorporated in the prod-

uct, the programs are written into a relatively inexpensive

component called masked ROM, which cannot be rewritten.

In reality, however, program revision often continues un-

til just before product shipment due to the modification of

specifications or bugs found during development. In such

cases, the use of masked ROM entails huge revision costs.

Furthermore, since the production of masked ROM requires

a certain amount of time, product shipment can be delayed

when revisions have to be made.

Recently, microcontrollers with rewritable built-in flash

memory have been adopted in place of masked ROMs in anincreasing number of cases in order to provide for some lee-

way in the development schedule, even if slightly increasing

the cost. Thus, microcontrollers with built-in ash memory

are currently on the market in large quantity and have be-

come more aordable.

When selecting a microcontroller with built-in ash mem-

ory, you need to be careful about the ash memory capacity.

First, you have to make a rough estimation of the program

capacity based on the product specifications, and then

choose a microcontroller with a memory capacity somewhat

larger than the estimate. Furthermore, if you have options

about the capacities of built-in ash memory for the same

microcontroller, you can continue development even if the

planned program capacity is exceeded. The cost slightly

uctuates if the capacity is changed, but you can still meet

the delivery date. Accordingly, do not forget to check on this

point as well.

When manufacturing the product, you also need to conrm,

in advance, by whom and how the programs will be written

to the ash memory. If a special tool is required to write the

programs, you have to add the cost of this tool as well. If the

programs are written by the microcontroller manufacturer

before delivery, you should check the schedule to hand over

the nal program data to the manufacturer and the schedule

of component delivery. These schedules also serve as the ba-

sis for making a decision in selecting a microcontroller.

[ Development Assets ]

Reuse Circuits and Software

When you develop a microcontroller-equipped product, all

kinds of expertise will be accumulated during that time. For

example, you may have to modify the timing to supply clock

signals or the power supply circuit so that the microcon-

troller can be stably reset. In fact, these pieces of knowledgeare all regarded as development assets.

The programs that operate the microcontroller are some-

times referred to as software, and this software can also be

reused as an asset. For example, if you developed or pur-

chased middleware to process a certain kind of signal, the

same software can be applied continuously to products that

need the same function. In other words, microcontrollers on

which the software was developed and runs stably will con-

tinue to be selected.

In corporate activities, it is necessary to reuse assets

achieved through investment in development as much as

possible. Thus, once a microcontroller including other mod-

els from the same series is selected, it tends to be selected

continuously.

Note here that you must choose the right microcontroller

that can meet the requirements demanded for the product

under development. To make full use of previously adopted


14/31

24


25

microcontrollers and the resulting development assets, there

are often cases where the microcontroller and development

assets were set as the starting point in designing product

specications, which is a preposterous idea. Products devel-

oped in such a way can end up as a failure in terms of sales

because they cannot ensure sucient customer satisfaction

even though they result in lower investment cost.

Thus, it is important to select a product released by a

manufacturer that is continuously expanding its lineup of

products and middleware. It is strongly recommended that

you check manufacturer roadmaps and strategies. Of course,

it goes without saying that you should modularize the cir-

cuits and software created in-house so that you will be able

to reuse them in the future.

In view of such circumstances, you need to plan a medium-

to long-term development strategy for the product and care-fully select a microcontroller.

[ Development Environment ]

Pay Attention to Compiler Performance and

Cooperation with Debugger

A compiler and a debugger are necessary tools in the de-

velopment of programs to operate the microcontroller.

A compiler is a tool to convert source code written in C,

etc., into programs that can be read into the CPU. Compiler

performance affects the performance and quality of pro-

grams, so you need to check in advance whether a compiler

suitable for the microcontroller is available.

For example, you may nd yourself in trouble if the perfor-

mance of the compiler optimization option function, which

reduces the program capacity or increases the processing

speed, is unsatisfactory, because then the planned program

size may be exceeded or the expected responsiveness may

not be ensured. Furthermore, a compiler is also software and

may have bugs. Thus, it is important whether the compiler

vendor has a sucient support system.

When selecting a microcontroller, you have to make sure

that a trouble-free compiler is available so that you can con-

centrate on the development work originally intended.

A debugger is a tool used to verify whether a program

works correctly. A device called an in-circuit emulator (ICE)

is connected to the target board equipped with the micro-

controller and the program operation is controlled while

communicating with special application software.

In particular, when using the Joint Test Action Group in-

circuit emulator (JTAG-ICE), eciency in development varies

signicantly depending on whether the microcontroller itselfhas a debugging support function. JTAG-ICE is a tool used

to expand JTAG control functions and enables users to read

data from or write to the registers and memory in the CPU

and execute the steps of a program. Regarding the trace func-

tion used to analyze bugs, for example, various schemes are

provided in some microcontrollers in order to obtain detailed

trace results. If the trace function is unsatisfactory, the behav-

ior of the microcontroller cannot be analyzed properly and

thus you may go through a lot of trouble in debugging work.

As outlined above, the development environment is an

extremely important factor for engineers. When selecting a

microcontroller, always make sure to check the support con-

ditions of your development environment.

Make Long-Term Considerations Including

Maintenance Period

The functions and performance required for devices vary

widely depending on the application and use conditions.


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26 27


Microcontrollers often play an important role in the devices.

Accordingly, you have to carefully select a microcontroller

that serves this purpose by focusing on the functionality and

performance covered by the points in this article.

In addition to selecting a microcontroller that meets func-

tional and performance requirements, you must remember

to consider every aspect to manufacture the target product,

such as the cost, delivery period for parts procurement and

whether the parts can be stably supplied during the produc-

tion and maintenance periods of the device.

27

The World's First Microprocessor

Born of the Calculator Wars

"The 4004"It was in 1971 that the worlds

first microprocessor, the Intel

4004, appeared. The 4004 pro-

cessor was born as the core of

the "MCS-4" chipset developedby Intel at the request of Busi-

com, a Japanese calculator manufacturer. At that time,

Intel was only a four-year-old company.

In June 1969, Masatoshi Shima and two other Busi-

com engineers were sent to develop a general-purpose

LSI for calculators in collaboration with Intel. Although

Busicom proposed an architecture using "macroinstruc-

tions" defined by finely breaking down the functions

of a calculator, an investigation carried out by Intel

revealed that the architecture would require at least 10

chips.To overcome this situation, Ted Hoff from Intel pro-

posed a method in late August 1969 to use a 4-bit CPU

and constitute a calculator by using "microinstructions,"

which have a higher degree of versatility. This became

the prototype of the 4004.

Aside from Shima and Hoff, Federico Faggin from

Intel joined the development team and the design work

intensied from April 1970. The team started shipping

samples of the 4004 in March 1971.

Faggin noticed the high versatility of the 4004 and

persuaded Intel executives to negotiate with Busicom

for the direct sales rights. Busicom accepted the pro-

posal on the conditions that Intel pay back part of the

development cost and not sell the microprocessor to

other calculator manufacturers. This was because Busi-

com was battered by escalating low-price competition

in the calculator market.

This event marked the beginning of the history of mi-

croprocessors.

The 4004microprocessor chip

NEHandbook2011

M

icrocontrollers


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28 29

Microcontroller Glossary

CPUControl of

program

execution

Management of

instruction

to be executed

Execution of

instructions

for data

Data retention

before and after

operation

Microcontroller

Main

memory

Flash

memory

Peripheral

circuit

External bus

Program counter

Instruction register

Instruction decoder

General register

Address

Data Data

DataData

Arithmetic

and

logic unit

(ALU)

Main components constituting a CPU

Word 01

actual fact, the classication is not that strict.

In general, microcontrollers are often classied according

to the operation data width of the ALU in the CPU. However,

there are various components in the CPU that operate with

dierent bit widths and they may not coincide with the oper-

ation data width of the ALU. To be more precise, this includes

the widths of registers in the CPU, the widths of external ad-

dress and data buses and the widths of instructions executed

by the ALU. In some models, for example, the ALU operation

data has a width of 32 bits and the external data bus is 16

bits wide. This difference results from how the circuit area,power consumption and computing performance, etc., are

balanced.

The classication according to the bit count is just for the

sake of convenience. When actually selecting a microcon-

troller, one must carefully determine which part of the inter-

nal structure of a microcontroller the bit count species.

A central processing unit (CPU) is a circuit that carries

out basic arithmetic operations and data transfer, etc., in ac-

cordance with the instructions of computer programs. It iscomposed of an arithmetic and logic unit (ALU) to execute

actual operations, registers to temporarily store data and in-

structions and circuitry to control the execution of programs.

In addition to the CPU, a microcontroller is equipped with

main memory, ash memory and various kinds of peripheral

circuits.

A program is executed in the CPU as described below.

First, the memory address of the instruction to be executed

is fetched from the program counter and the instruction is

read into the instruction register. Then, the instruction is con-

verted (decoded) into an instruction executable by the CPU.The value of the general register, the value in the specified

main memory location and the value directly specied by the

instruction are used as operands. Based on the instruction

and the data, the ALU carries out the operation and writes

the results to a register or the main memory. The procedure

is repeated in the order specied by the program.

The CPU also has circuits to branch or interrupt a program.

If the program includes a branch, a judgment based on the

preset condition is made using a ag register that stores the

status of operation and the process ow jumps to another in-

struction if the condition is met. An interrupt controller con-

trols interrupt processing to interrupt the current process if aspecic signal is received and to resume the original process

when a series of other processes has been executed.

Various Denitions for Microcontroller Bit Count

Microcontrollers may be classied using terms such as 8-

bit, 16-bit and 32-bit based on the CPU specications. In

CPU


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30 31

Floating gate structure

SourceDrain SourceDrain

Floating gate

Control gate

MONOS structure

Control gateBlockinsulating film

Tunnelinsulating film

Nitride film

Noncovalent bonds in nitride film

Asymmetric multiprocessing

CPU0

Memory

space 0

CPUn

Memory

space n

Symmetric multiprocessing

CPU0

Memory space

CPUn

Structures of embedded ash memory

(illustration courtesy of Renesas Electronics)

Embedded Flash Memory

Two implementation forms in multi-core environment


Embedded flash memory is flash memory formed on the

same die on which the CPU and other logic circuits are provid-

ed. While microcontrollers equipped with masked ROM, whereprograms are written on a mask, have been pervasive thus

far, most recent products come with embedded ash memory,

where programs are written and used by device manufacturers.

There are mainly two types of embedded ash memory. One

is the oating gate structure that stores electric charges in a

semiconductor layer covered by an insulating lm. The other

is the metal-oxide-nitride-oxide-silicon (MONOS) structure that

stores charges in traps distributed in a nitride lm covered by

an insulating layer. (Instead of MONOS, the term SONOS,

with the rst word replaced by silicon, is sometimes used.) In

general, it becomes harder to form the insulating lm and thecontrol gate in the oating gate structure as the miniaturiza-

tion progresses. Meanwhile, the MONOS structure is thought

to have a problem with data retention properties. Renesas Elec-

tronics selectively uses embedded ash memory of both types.

The company chooses the floating gate structure when low

power consumption and low-voltage operation have priority,

whereas the MONOS structure is chosen when a large capacity

and high-speed operation are prioritized.

Word 03Word 02

Multi-core refers to a technique to mount two or more

CPUs on a semiconductor such as microcontroller. Multi-core

technology is already commonplace for microprocessors usedin personal computers and mobile devices. Recently, multi-

core microcontrollers are being commercialized.

There are two reasons why multi-core technology is being

promoted. First, there is a demand to integrate multiple sub-

systems for the cost reduction of entire devices. This is the

main demand in the case of microcontrollers. By adopting the

form of asymmetric multiprocessing (AMP) in which multiple

CPUs have dierent memory spaces, the subsystems can be

integrated without significantly changing the program. The

integrated CPUs may be of the same or dierent types.

Another reason is that, as miniaturization in semiconductor

production technology progresses, power leakage tends to

increase when the operating frequency is raised. As a result,

multi-core architecture has been promoted as a method to

enhance the processing performance of a microprocessor

without increasing the power consumption. In this case, an

implementation form of symmetric multiprocessing (SMP) is

often adopted in which multiple CPUs share the same memo-

ry space.

Multi-Core


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32 33

Task

OS(kernel)

User program

Programs of services(network functions, etc.)

provided by OS

Task management(generation, activationand switching of tasks)

Inter-taskcommunication

(event flag,semaphore, etc.)

Processing of varioustypes of APIs

(memory, time andinterrupt management)

Programs of I/Odevice processing

and interrupt processing

Example of integrated development environment using

Eclipse (Picture courtesy of Wind River)

Integrated Development Environment

Typical structure of real-time OS


An integrated development environment is a software de-

velopment environment that integrally provides the required

tools. It includes a source code editor, a compiler to convertsource code into object code, a linker to convert the object

code into an executable form and a debugger to execute the

programs in a stepwise manner and display the contents of

various types of registers and memory.

In the development of microcontroller software, an emula-

tor connected to a microcontroller via the Joint Test Action

Group (JTAG) interface is often used. It is a piece of hard-

ware that enables users to check functions including the

actual I/O control, while making the microcontroller operate

at the same speed as the actual setup. As a result, the debug-

ger included in an integrated development environment formicrocontrollers usually has the capability to operate in con-

junction with an emulator.

Recently, an increasing number of embedded OS vendors

are using Eclipse, an open source integrated development

environment. Eclipse is distributed to embedded OS users

with dedicated plug-ins such as a compiler and a debugger.

A real-time operating system (OS) is a type of OS that em-

phasizes the strict management of the time at which a pro-

gram is executed. There is no quantitative denition of whatexactly is real-time, but some of the requirements of a real-

time OS are: capable of ensuring the worst-case length of

time spent to call an interrupt processing program after the

occurrence of a hardware interrupt and capable of ensur-

ing the scheduling to rst execute the task with the highest

priority.

The basic functions of a typical real-time OS are: (1) the

task management function to generate and activate tasks as

well as execute scheduling; (2) the inter-task communication

function to enable synchronization and messaging between

tasks; and (3) the processing function for various types ofapplication programming interfaces (API), such as memory,

time and interrupt management. In addition to these basic

functions, many real-time OS vendors provide a communica-

tion protocol stack and other programs as added functions.

In a strict sense, they are not the core portion of the OS

(kernel). These programs run as tasks of the OS, just like the

programs created by device developers.

Word 05Word 04

Real-Time OS


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34 35

Source code

in assembly language

Assembler

Object code (machine language)

based on instruction set architecture

Source code in C

Compiler

Instruction

Data type

Register structure

Addressing method, etc.

Instructionset architecture

Relationship between instruction set architecture

and programming language

Instruction Set Architecture


An instruction set architecture defines the CPU instruc-

tions, data type, register type, memory structure and ad-

dressing method for the operands, etc. It can be describedas the CPU specifications from the perspective of software

developers and compilers. The CPU design that indicates the

kinds of circuits used to implement the instruction set archi-

tecture is called microarchitecture.

In the development of microcontroller programs, assembly

language or C is used. Assembly language uses instructions

that correspond to the CPU object code (machine language)

on a one-to-one basis, whereas C uses a compiler to convert

the source code into object code. Assembly language is close-

ly related to the instruction set architecture and thus it is dif-

cult to port programs from one CPU to another once theyare written. However, as programming in C, etc., is becoming

popular, the dierences in CPU instruction set architectures

can be overcome by a compiler. Constraints such as the need

to use products from the same series in order to properly

run old programs are gradually being eliminated.

A digital signal controller is a microcontroller with an

enhanced capability to process digital signals. Because it

employs the elements of a digital signal processor (DSP) atthe architecture level, e.g., a multiply-and-accumulate (MAC)

operation execution unit, it is sometimes called a DSP micro-

controller. The integration of a DSP and a microcontroller

was originally promoted with the main purpose of eectively

carrying out media processing, but lately DSCs are also at-

tracting attention in the field of feedback control applica-

tions for motors and power supplies.

Currently, DSCs are spreading widely because of two as-

pects. One of the aspects is that an increasing number of

general-purpose microcontrollers are becoming capable

of performing MAC and other operations with the use of adedicated unit. Most DSCs released thus far are specialized

for motor control, etc., but the development of ARMs Cortex-

M4, a CPU dedicated for microcontrollers also equipped with

DSP instructions, led several semiconductor manufacturers

to commercialize general-purpose microcontrollers that can

be used as DSCs. These products have an advantage in that a

system capable of performing motor control and audio pro-

cessing can be built without the use of an external DSP.

The other aspect is that DSCs designed for digital power

supply control have become available at low prices. Models

equipped with a CPU that supports digital signal processing

instructions, a high-speed pulse-width modulation (PWM)

unit, an analog-to-digital (A/D) converter, etc., have become

as aordable as general-purpose microcontrollers. This can

lead to the rapid spread of the use of digital power supplies,

which contribute to the size reduction and efficiency im-

provement of power supplies.

DSC

Word 07Word 06


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36 37

Major serial communication interfaces supported by microcontrollers

Serial Communication Interface

Classifica-

tion

Name of standard Numbe r

of signallines

Notes

Asynchro-nous

UART (universalasynchronousreceiver-transmitter)

3 Applicable to LocalInterconnect Network(LIN), etc.

Synchro-nous

I2C (inter-integratedcircuit)

2 Proposed by Philips.First standardized in1992.

SPI (serial periph-eral interface)

3 Proposed byMotorola.


A serial communication interface is a communication inter-

face that sequentially transmits data one bit at a time via one

signal line. Most microcontrollers integrate a universal asyn-chronous receiver-transmitter (UART), which is a transmitting

and receiving circuit for asynchronous serial communica-

tion, or a universal synchronous and asynchronous receiver-

transmitter (USART), which is based on the UART but with an

additional circuit for synchronous serial communication.

The UART is mainly used for the asynchronous serial com-

munication of microcontrollers, whereas the I2C and serial

peripheral interface (SPI) are often used for synchronous

serial communication. In addition, three-wire synchronous

serial communication to communicate on a one-to-one basis

is sometimes utilized. The universal serial bus (USB) andEthernet supported by some microcontrollers are also serial

communication standards.

The parallel communication interface, which simultane-

ously transmits multiple-bit data via a number of signal lines,

has a problem in that it uses many signal lines and the tim-

ing can easily uctuate during high-speed operation. Accord-

ingly, serial communication has been increasingly used in

recent years.

Circuits that handle continuous electric signals are col-

lectively called analog circuits. Typical analog circuits used

in a microcontroller are analog-to-digital (A/D) and digital-to-analog (D/A) converters. This is because a microcontroller

frequently receives input signals from sensors and outputs

signals to actuators. A power-on reset (POR) circuit is an-

other analog circuit. It monitors the supply voltage of the

system and initializes the microcontroller when the preset

voltage is reached.

In particular, the A/D converter is an indispensable func-

tion of a microcontroller. Models with a resolution of 8-16

bits are commonly employed. Successive approximation

type A/D converters, which repeatedly execute magnitude

comparison with one comparator, and -type converters,which integrate the analog signals that have been subjected

to oversampling and then quantize and dierentiate the re-

sultant signals, are used.

There have been moves to reduce the number of compo-

nents, mounting surface and power consumption by incor-

porating analog IC circuits inside a microcontroller, instead

of using them around the microcontroller. A number of semi-

conductor manufacturers have commercialized microcon-

trollers that incorporate, for example, an operational ampli-

er to amplify analog input signals when the signal voltage

is extremely low, a comparator for overcurrent/overvoltage

protection and a drive control circuit for the liquid crystal

panel.

Analog Circuit

Word 09Word 08


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38 39

Genealogy of Microcontrollers

Microcontroller-Dedicated CoresDerived from General-PurposeProcessor Cores

ARM processors are widely used as microcontrollers, as

well as processors for mobile phones and other portable de-

vices, but they have a somewhat complicated family line.

The original ARM was a 32-bit reduced instruction set

computer (RISC) architecture, which was developed by Acorn

of the U.K. for its personal computers. This instruction set

is called ARM V1. Later on, Acorn's development team was

spun off as Advanced RISC Machines (currently known as

ARM) and converted its business to sell processor cores. Its

first product was the ARM6, followed by the release of the

ARM7 and ARM8.

A 16-bit reduced instruction set called "Thumb" was added

to the ARM9. The ARM7 TDMI, widely used as a general-

purpose microcontroller, was a variant of the ARM7, which

was modied based on the ARM V4 architecture adopted in

the ARM8 and ARM9.

ARM then released the ARM10 equipped with the ARM

V5 architecture and the ARM 9E, a modied version of the

ARM9 based on the ARM V5 architecture. Next, the company

released the ARM11, which was based on the ARM V6.

The latest version of the instruction set is ARM V7 released

in 2005. After the adoption of ARM V7, all the products are

named with a unied style, "Cortex-XYY." Here, the letter "X"

denotes the usage where "A," "R" and "M" represent applica-

tion, real-time control and microcontroller, respectively. The

letters "YY" denote the numbers that represent the position

of the product.

ARM MIPS Renesas Freescale

ARM1Forapplicationprocessors

Forreal-timecontrol

Formicrocontrollers

Basicinstruction set

For FPGAs

ARM2 ARM6

StrongARM

ARM8 ARM10

ARM9E

ARM3 ARM7

ARM7TDMI

ARM9

ARM V1 ARM V2 ARM V3

Thumb

ARM V4 ARM V5


22/31

40 41

The Cortex-A series includes the Cortex-A8, -A9 and -A5.

The Cortex-A8 is the rst model equipped with the ARM V7

series. The Cortex-A9 is compatible with multiprocessors and

the Cortex-A5 is an entry-level model. The Cortex-R series also

includes the Cortex-R4, -R5 and -R7. The Cortex-R4 features a

high-speed interrupt processing capability and the Cortex-R5

and Cortex-R7 are advanced models of the Cortex-R4.

The Cortex-M series is intended for microcontrollers.

Although the ARM7TDMI was widely used as a general-pur-

pose microcontroller, it was far behind the microcontrollers

from competing manufacturers in terms of performance. As

a breakthrough, ARM put the Cortex-M3 on the market. Al-

though it is a high-performance 32-bit microcontroller, it is

capable of providing a code density almost as high as that of

a 16-bit microcontroller through the adoption of "Thumb-2,"

the successor technology to Thumb. In addition, the die size

is almost as small as that of a 16-bit model. With such fea-

tures, ARM is vigorously attempting to make users transit

from other manufacturers' 16-bit microcontrollers.

ARM also released a low-end model named the Cortex-M0.

While featuring a performance comparable to that of a 16-bit

computer, it is intended to be sold at a price as low as that of

an 8-bit microcontroller and operated with equivalent power

consumption. In addition, the Cortex-M4, a variant of the Cor-

tex-M3 equipped with a digital signal processor (DSP) exten-

sion, is available for high-end applications. With these three

products, ARM is reportedly aiming to gain a 20% or larger

share in the microcontroller market sometime in the future.

The Cortex-M1, designed based on the Cortex-M3, is avail-

able as a software core that operates on eld programmable

gate arrays (FPGA). The Cortex-M1 is licensed to major FPGA

vendors and end users who have bought the FPGA from

these vendors can use the Cortex-M1 without a license.


ARM10

ARM9E

ARM11

Cortex-M1

Cortex-A8

Cortex-R4

Cortex-M3I

Cortex-A9

Cortex-A5

Cortex-R5

Cortex-R7

Cortex-M4

Cortex-M0

Cortex-A15

ARM V5 ARM V6

Thumb-2/NEON

Jazelle

ARM V7

Forapplicationprocessors

Forreal-time

control

Formicrocontrollers

Basicinstruction set

For FPGAs


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42 43

R2000

MIPS MIPS

R3000 R6000 R5000

MIPS MIPS

R4000 R8000 R10000 R12000


Began as Processors forWorkstations, Now PrimarilyUsed for Embedded Applications

MIPS processors have their origin in the MIPS project led

by John L. Hennessy of Stanford University. The architecture

developed by this project was commercialized by MIPS Com-

puter Systems, a company founded by Hennessy in 1984.

The company was purchased by Silicon Graphics (SGI) in

1992, but was later spun o as MIPS Technologies.

The products initially released by MIPS were not intended

for embedded applications, but for workstations. From its

rst product, the R2000, to the R12000, etc., the company

targeted high-performance processors.

Meanwhile, the MIPS core had been offered for embed-

ded applications since around 1990. Similar to the business

model of ARM, the company started licensing the core de-

signs, which turned out to be a great success. In 1997, the

shipment volume of MIPS processors overtook that of the

68000-based processors from Motorola Inc., becoming the


most widely used embedded processor in the world.

When it was spun off from SGI, MIPS redesigned the

architecture so that its core could be more easily used for

embedded applications. Before this modication, four types

of architectures, MIPS I to IV, had been defined. The MIPS

series had a structure in which MIPS I and II were provided

as the base architectures and MIPS III and IV were designed

to have additional instruction sets and functions while main-

taining backward compatibility. The company later changed

this structure to one similar to ARMs. The four architectures

were integrated into two instruction sets, MIPS32 (32 bits)

and MIPS64 (64 bits) and extensions were added as an op-

tion. MIPS32 comes in two families: the 4K family for micro-

controllers and the 20K family with enhanced performance.

The 4K family includes: the 4K, a basic 32-bit core that has

a similar structure to the R3000; the M4K, a low-end model;the 4KE, a high-speed model and the 4KS, which features a

built-in security function.

The 4K is further divided into three types. The basic one

is the 4Kp core. The 4Km core is based on the 4K and is

equipped with a high-speed multiplication and division


24/31

44 45

MIPS32 MIPS32 Release 2

ASEapplication specific extension

MIPS32

4K/4KE/4KS

MIPS32

24K

microMIPS

MCU ASE

MIPS32

M4K

MIPS32

M14K/M14Kc

MIPS32

24KE

MIPS32

1004K

MIPS32

34K

MIPS32

74K

MT ASE

DSP ASE

MIPS32

1074K


unit. The 4Kc core is based on the 4Km and incorporates a

translation lookaside buer memory management unit (TLB

MMU).

The low-end M4K core consists of only 35K gates. The 4KE

supports bit field instructions and vectored interrupts and

reduces the granularity of clock gating. It also supports a

write back function by increasing the maximum cache capac-

ity. With these features, the 4KE enables a high level of per-

formance. As with the 4K, it comes in three types: the 4KEp,

4KEm and 4KEc. The 4KS core also supports cryptographic

accelerator instructions (SmartMIPS ASE).

As for the 20K family, the MIPS32 24K, designed based

on the MIPS32 20K and equipped with an enhanced internal

structure, was released in 2003. The company also released

the MIPS32 34K in 2006 and the MIPS32 74K in 2007. The

MIPS32 34K is based on the MIPS32 24KE and enables si-

multaneous multi-threading (SMT). The MIPS32 74K is the

successor to the MIPS32 24KE and features an improved

internal structure.

Then in 2008, the MIPS32 1004K, which integrates up to

four MIPS32 34K cores, was released and was followed by

the release of the MIPS32 1074K in 2010, which integrates

four MIPS32 74K cores.

It should be noted that all of the MIPS32 models have a

reduced instruction set called MIPS16, which is similar to

ARMs Thumb. The company later dened a new instruction

set called microMIPS because MIPS16 has not been widely

implemented and released the MIPS32 M14K and M14Kc

incorporating microMIPS in 2009.


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46 47

PD780

etc...

V20/V25

V30

78K/0 78K0 V850ES

V830/V831

/V832

78K/ 78K0R V851V852/V853

/V854

78K// V850E1 V850E2

V40 V55 V805/V810 V820/V821

V35/V35+ V50V60/V70

/V80

V53/V53AV33/V33A

NEC 8-bit NEC 32-bit

NEC 16-bit


Multiple Product Lines with Ori-gins in Three Companies, Likelyto be Integrated in One Line

Renesas Electronics is a manufacturer that was formed by

a merger between NEC Electronics and Renesas Technology

Corp. Because Renesas Technology was founded as a result

of a business merger between the semiconductor divisions of

Hitachi and Mitsubishi Electric, the new Renesas Electronics

has coexisting product lines that have origins in three com-

panies.

First, there are the product lines of the former NEC Elec-

tronics. Their origins go back to the PD780, a Z80-com-

patible 8-bit processor and the V30, a 16-bit processor that

is upwardly compatible with the 8086. These processors led


to the 78K family/RL78 series and the V850 family, which

remain in use today.

While the PD780 was a stand-alone processor, the 78K

family was released as a one-chip microcontroller incorpo-

rating ROM, RAM and peripheral circuitry. Although a line

of high-end products was released, the low-end models, the

78K0 and 78K0S (initially called the 78K/0 and 78K/0S),

turned out to be pervasive. In 2006, the company released

the 78K0R, which was based on the 78K0 and equipped with

a 16-bit internal structure. It is still available today.

The V30 is famous for once being used in NECs PC-9801

series. The V60 and later versions are no longer compatible

with the 8086. In addition, the company adopted a 32-bit

RISC architecture starting with the V800 family, replacing

the CISC architecture that had been used until then.


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48 49

H8/500

SH-1

H8/300 H8/300L

H8/300H H8S/2000

H8/300H

Tiny

SH-2

SH2-DSP

SH-2A

SH-3 SH-4 SH-4A SH-X1

SH-X2

SH-X3

SH3-DSP

SH2A-FPU H8SX/1x00

Hitachi 8-bit

Hitachi 16-bit

Hitachi 32-bit


Next was the V850 family, which has much in common

with the V800 in terms of structure, but it is not compatible

with V800 in the strictest sense. The V850E (later renamed

to the V850E1) was designed based on the V851, which is

the first product from the V850 family and was modified

to enhance its speed. This product family also includes the

V850E2, which is equipped with a superscalar architecture

that enables simultaneous execution of two instructions and

the V850ES, which focuses on low power consumption and

low cost. They have been incorporated in various products

and are still in use today.

It shoul d be note d that NEC, as a partner of MIPS

Computer(currently known as MIPS Technologies), once re-

leased a product line called the VR series, which adopted the

MIPS architecture. However, the series consisted of old prod-

ucts compliant with MIPS III and IV. Currently, only a limited

part of the line is available for maintenance purposes.

After this come the former Hitachi product lines. The H8

series is the line that was independently developed by Hi-

tachi. The company rst released a 16-bit product called the

H8/500, followed by a reduced version, the H8/300. The

H8/300H was developed by extending the H8/300 architec-

ture to 16 bits, but in a dierent way from the H8/500. Both

the H8S/2000 series, which is a version of the H8/300H fea-

turing enhanced speed and the H8SX/1x00, which is a 32-

bit version of H8S/2000, are still in use today.

The Super-H is a 32-bit RISC processor completely dier-

ent from the H8 series. Although the Super-H is designed

with address and data lengths of 32 bits, its instruction

length is xed at 16 bits, thereby increasing the code density.

A memory management unit (MMU), which was not incor-

porated in the SH-1 and -2 series, was included with the SH-

3. The SH-4, a version of the SH-3 with enhanced speed, was

also provided with a single instruction multiple data (SIMD)type oating-point unit (FPU). The SH-X1, a system-on-chip

(SoC) core for embedded applications developed by modify-

ing the SH-4, was released after the company was reborn as

Renesas Technology. This was followed by the release of the

SH-X2, a version of the SH-X1 with enhanced speed and the

SH-X3, a multi-core-enabled version. They are used for SoC

in mobile phones and other devices.


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50 51

M16C M16C

M32C

78K0R

Mitsubishi 16-bit

M32C

M32R

Mitsubishi 32-bit

R8C/1x R8C/2xR8C/3xR3C/LxR3C/Mx

RX200

Renesas Technology 16-bit

R32C/80 R32C/100

RX600

Renesas Technology 32-bit

RL78

Renesas Electronics 16-bit


The former Mitsubishi Electric product lines are rather

simple. Mitsubishi released three types of cores: the M16C,

M32C and M32R. The M16C is a 16-bit core and the M32C

is a 32-bit version of the M16C. The M32R is a modied ver-

sion of the M32C and is adapted to control purpose. Based

on these cores, a wide range of products combining periph-

eral circuits, etc., are available. The M16C and M32C are still

widely used today.

Together with the merger of the companies, there have

been moves to integrate these products. For example, the

R8C series, which combines the M16C core and the H8S pe-

ripheral circuitry, was commercialized so that users of both

products could make a smooth transition. The R32C was

released to facilitate a similar transition by combining the

M32C core and peripheral circuitry equivalent to that used

in the R8C.

Following the launch of these products, Renesas Technol-

ogy announced in 2007 the development of the RX family,

a line of entirely new CISC-based processors. The company

rst released a 32-bit processor called the RX600, followed

by the 16-bit RX200 processor. The products were designed

with the intention to integrate the companys middle-range

CISC architectures into one family in the future. However,

the plan was somewhat derailed by the merger with NEC

Electronics in 2010.

The RL78 was the rst product developed by Renesas Elec-

tronics after the merger. It combines the 78K0R core and the

peripheral circuitry of the R8C. As of March 2011, however,

it still uses 78K0R-based peripheral circuitry. A series of

products remodeled with the use of R8C-based peripheral

circuitry is slated for launch.


28/31

52 53

MC6800

MC6801/6803

MC68328DragonBall

MC683xxQUICC

68HC16 56800/E 56F8000

MC6809 MC68030

MC88000

MC68040 MC68060

ColdFire V2 ColdFir

MC68010 MC68020MC68000/MC68008

MC68VZ328DragonBall VZ

MC68SZ328DragonBall

Super VZ

MC68EZ328DragonBall EZ

68HC11 HCS12 HCS12X68HC12

68HC05MC6805 HCS08HC08

RS088-bit microcontroller

16-bit microcontroller

32-bit processo r/micr

ocontroller


Worlds First Developer of One-Chip Microcontroller Gains Edge inApplications for Automobiles and

Communication DevicesFreescale Semiconductor was the first company in the

world to manufacture a one-chip microcontroller. More pre-

cisely, the forerunner of Freescale, i.e., the semiconductor

division of Motorola, Inc., manufactured the worlds rst one-

chip microcontroller named the MC6801. The MC6801 inte-

grated the MC6800 8-bit processor, ROM, RAM, a 16-bit tim-

er, parallel I/O and serial I/O into a single chip. Its successor,

the MC6803, was used for a wide range of applications. The

MC6803 was then followed by a modied version (MC6805),

a CMOS version (68HC05) and its successor the HC08. The

RS08 is the low-priced version of the HC08 and the HCS08 is

the high-end version. Combined with the ColdFire processor


described below, the RS08 and HCS08 constitute a product

line called Flexis. The use of common peripheral circuits fa-

cilitates the transition from 8-bit to 32-bit architecture.

The 16-bit products are classified into two family lines.

One is the MC68000 family, which was used in Macin-

tosh computers, etc. and the other is the 68HC11 family,

which was developed by modifying the MC6801 separately

from the MC6805. The 68HC12 is a 16-bit version of the

68HC11. The HCS12, a modied version of the 68HC12 and

the HCS12X, the successor to the HCS12, are still available

as 16-bit microcontrollers for automotive applications.

There is also a unique product called the 56800/E, which

adds the functions of a microcontroller to a 16-bit DSP. The

56F8000 series is designed based on the 56800/E core and

is equipped with integrated peripheral circuitry. Freescale

stopped the development of new products for this line, but


29/31

54 55

MC68060 ColdFire V5

ColdFire V1

ColdFire V2 ColdFire V3 ColdFire V4 ColdFire V4e

32-bit processor/microcontroller

MPC603eG2

e300

PowerPC Classic

PowerISA

e700

e500mce500

e5500

e200 e200Z

e600

MPC7400G4


the company is still providing existing models.

As for 32-bit products, the company released a MC68000-

based model called the MC68030, as well as its successor

the MC68040, but the development of the MC68040 oun-

dered. As a result, the MC68040 fell far behind its main

competition, the 486 from Intel Corp. Yet, the 68000 archi-

tecture had a large share of the market for embedded pro-

cessors at that time. Accordingly, the company redesigned

the 68040 core based on RISC architecture and developed

ColdFire, targeting the embedded application market. First,

the V2 was released and followed by the V3, V4 and V5,

modied versions with enhanced functionality. These cores

are mounted on a number of 32-bit microcontrollers.

The PowerPC family is another 32-bit product line. The

first product from this family was the MPC603e. Freescale

developed the e300 core based on the MPC603e and the

e600 core based on the MPC7400 and used them in a num-

ber of microcontrollers in communication devices and auto-

mobiles.

However, the architectures of the e300 and e600 were

intended for use in personal computers and were not neces-

sarily suited for embedded applications. To overcome this

problem, a nonprofit standard-setting organization called

Power.org was established and the organization dened the

PowerISA standards. Freescale newly developed the e200

core, which is compliant with the standards and decided to

make a shift to this core in principle. The e200 core was en-

tirely adopted in the Qorivva microcontroller series for auto-

mobiles and is also used in the PX microcontroller series for

industrial and general-purpose applications. The company

also developed the e500 core, which is a higher-end version

of the e200 and the e500mc core, which is a multi-core-

enabled model. It also developed a 64-bit core called thee5500. The QorIQ microcontroller series for communication

devices uses these cores exclusively.


30/31

NE Handbook series 2011 Microcontrollers

Publisher NikkeiBusinessPublications,Inc.

1-17-3Shirokane,Minato-ku,

Tokyo108+8646Japan

Published April,2011

Editor NikkeiElectronics

Design NikkeiBPConsulting

Printing DaiNipponPrinting

Sponsoredby Digi-KeyCorporation

NikkeiBusinessPublications,Inc.2011

Allrightsreserved.PrintedinJapan

About the Authors

"Guidelines for Selecting a Microcontroller

with Required Functions and Performance"pp. 6-26

Norikazu KunikataDevelopment Technology Promotion Group of Teac Corp.

Joined Teac in 1989. He was in charge of the design of analog

and digital circuits for audio equipment, as well as board design,

etc. He has been involved in the development of HDD recorder

software since 1998. He has also worked on quality improvement

activities and human resource development. He is a member of the

Society of Embedded Software Skill Acquisition for Managers and

Engineers (SESSAME).

Genealogy of Microcontrollers pp. 38-55

Yusuke OharaFreelance technical writer

Mainly specializes in the architecture of CPUs, memory and

other components, as well as operating systems (OS), drivers and

rmware.


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