Digital Registers & Counters

Presented to: Submitted by: Inam ul Haq Zohaib Abbas (1006)Senior Lecturer Ume Farwa (1007)

Computer Science Mehwish Saleem(1008) Nida Javed (1009)Amtul Noor (1010)

BSIT-Mor-3rd

Latches(sipmple SR latch)• SR NOR latch• The most fundamental latch is the simple SR latch,

where S and R stand for set and reset and it is an asynchronous device.

• It can be constructed from a pair of cross-coupled NOR gates and NAND gatesbut the inputs are swapped and negated. In this case, it is sometimes called an SRlatch.

• The stored bit is present on the output marked Q. Therefore latches can be memory devices, and can store one bit of data for as long as the device is powered.

Simply a latch is an example of a bistable multivibrator, that is, a device with exactly two stable states. A latch has a feedback path, so information can be retained by the device as long as power is provided.

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• The state of S = R = 1 is "illegal" and should never be entered. The device will quickly exit the metastable state due to differences between the two gates .

• Other types of latches are Gates SR Latch, D Latch etc.

FLIP FLOPS

Flip flop is a basic memory element in a digital computer. It is used to store One bit of information with a 0 or a 1.

APPLICATIONS OF FLIP FLOPS:Flip flops have a wide variety of applications.Some are:

Digital Registers.

Digital Counters.

Digital Registers

Registers are groups of flip-flops, where each flip-flop is capable of storing one bit of information. An n-bit register is a group of n flip-flops.

The basic function of a register is to hold information in a digital system and make it available to the logic elements for the computing process.

A processor with 32-bit register can store 232 different values, the same applies with 64-bit register CPU.

Registers consist of a finite number of flip-flops. Since each flip-flop is capable of storing either a "0" or a "1", there is a finite number of 0-1 combinations that can be stored into a register. Each of those combinations is known as state or content of the register.

Registers are synchronous circuits and all flip-flops are controlled by a common clock pulse. As registers are often used to collect serial data they are also called accumulators.

Types of Registers

Shift Registers.Cyclic Registers.Parallel in serial out registers.

Shift Registers.

A REGISTER capable of shifting binary information in one or both directions.

Consists of a series of flip flops cascaded together with the output of one flip flop connected to the input of the other flip flop.

All flip flops receive common clock pulses that initiate the shift from one stage to the next.

They are generally provided with a Clear or Reset connection so that they can be "SET" or "RESET" as required.

Controlled with certain clock pulses by inhibiting the clock from the input of the register if shift is not required.

It is also able to provide extra circuits to control the shift operation through the D inputs of the flip flops rather than the clock input.

Shift Register Logical diagram

Cyclic register or Bidirectional

A register capable of shifting in one direction only is called unidirectional shift register. A register that can shift in both directions is called bidirectional shift register.Sometimes it is necessary to “recycle” the same values again and again. Thus the bit that usually would get dropped is fed to the register input again to receive a cyclic serial register.

Parallel in serial out register• The parallel data is loaded into the register

simultaneously and is shifted out of the register serially one bit at a time under clock control.

• The Parallel-in to Serial-out shift register acts in the opposite way to the serial-in to parallel-out one above. The data is loaded into the register in a parallel format in which all the data bits enter their inputs simultaneously, to the parallel input pins PA to PD of the register. The data is then read out sequentially in the normal shift-right mode from the register at Q representing the data present at PA to PD.

Parallel in serial out register logic Diagram

Counters

A register that goes through a predetermined sequence of states upon the application of input pulses is called a counter .

A counter that follows the binary number sequence is called binary counter. The main type of flip-flops used in counters are J-K flip-flops or T flip-flop.

Types of counters

Basically counters are of two types:• Asynchronous counter.• Synchronous counter.

Asynchronous counter

For these counters an external clock signal is applied to one flip-flop, and then the output of the preceding flip-flop is connected to the clock of the next flip-flop.

Synchronous counter

In synchronous counter all the flip-flop receive the external clock pulse simultaneously. Ring counter and Johnson counter are the examples of synchronous counters. in synchronous circuits, the external clock applied to all the flip flops is in synchronization with the circuit.

References:Fundamentals_of_Logic_Design_6th_2012Reference book - digital_design-

__morris_mano-fifth_edition.http://en.wikibooks.org/wiki/Digital_Circuits/

Registers_and_Countershttp://en.wikipedia.org/wiki/Register

Thank You…!