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I HC QUC GIA TP.HCH MINHTRNGI HC BCH KHOA

KHOAIN-IN TBMN KTHUTIN T

Embedded System Design

5. Software development for an embeddedsystem

11

.2. C Programming for PIC3. Timer and interrupt

1.Softwarediagram Software

diagram

isadiagramhelpsoftware

developersandprogrammanagerstointerpret

software a lication relationshi s actions and

processes.

Softwarearchitecturediagram:describesthehighlevelstructureofasoftwaresystem

Programflowchart:demonstrateshowaprogramworkswithinasystem

B mn K Thutin T -HBK

Dataflowdiagram:illustratestheflowofinformationinaprocess

Statemachinediagram:presentsdecisionflowsofastatemachine

2

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1.Softwarediagram

Drawasoftwarediagram: Usearectangleforaprocess

Useadiamondshapeforadecision

Useaparallelogramfordata

Usearectanglewithtwoverticallinesforpredefineprocess

N

B mn K Thutin T -HBK 3

Y

process terminator decision data predefine process

1.Softwarediagram Exampleforsoftwarearchitecturediagram Showtheconnectionsbetweenhardwareandsoftware

Showtheconnectionswithothersystems

S owt e nter acew t users

Examples


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1.Softwarediagram

Softwareblock

diagram

Example

State machine diagramProgram flowchart


1.Softwarediagram Dataflowdiagram(DFD)


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Groupdiscussion

Discusaboutbelowsoftwarediagram:START Decision block must have

YES/NO branches

InitLCD

Read

temperatureT

T>T_t? TurnOFF

heater

A process block must have 1input and 1 output


Oven control system

TurnONheater

Teamwork Drawasoftwarediagramforyourclassproject


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2.CprogrammingforPIC

Reference MartinBates,Programming8bitPICMicrocontrollers in

, ewnes,

ManyCcompilersforPIC:

MikroC (www.mikroe.com)

PICC18 (www.htsoft.com)


MPLABC18,C30 www.m croc p.com

CCSC(www.microchipc.com/reviews/CCS_C/)

9

Outline2.1PIC16CGettingStarted

Simpleprogramandtestcircuit

Variables,looping,anddecisions

2.4PIC16CSequenceControl

Whileloops

Break,continue,goto

If else switchSIRENprogram

2.2PIC16CProgramBasics

Variables

Looping

Decisions

2.3PIC16CDataOperations

Variabletypes

, ,

2.5PIC16CFunctionsandStructure

Programstructure

Functions,arguments

Globalandlocalvariables

2.6PIC16CInputandOutput

RS232serialdata

SerialLCD

Calculatorandkeypad


Floatingpointnumbers Characters

Assignmentoperators

2.7PIC16CMoreDataTypesArraysandstrings

Pointersandindirectaddressing

Enumeration

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2.1PIC16CGettingStarted

Microcontrollerprogramscontainthreemainfeatures:Sequencesofinstructions

Conditionalrepetitionofsequences

Selectionofalternativesequences

Listing 2.1 A program to output a binary code

/ * Sour ce code f i l e: OUTNUM. CAut hor , dat e, ver si on: MPB 11- 7- 07 V1. 0Pr ogr am f unct i on: Out put s an 8- bi t codeSi mul at i on ci r cui t : OUTBYTE. DSN

*******************************************************/


#i ncl ude "16F877A. h" / / MCU sel ect

voi d mai n( ) / / Mai n bl ock{

out put _D( 255) ; / / Swi tch on out put s}

11

Figure 2.1 MPLAB IDE Screenshot


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Figure 2.2 ISIS dialogue to attach program


SetupIOPorts Portmodes #usefast_io(port):leavesthestateoftheportthesameunlessre

configured

_ _ ,directionregisterfortheport

#usestandard_io(port):defaultforconfiguringtheporteverytimeitsused

Set

directions

set_tris_a(value);

value=get_tris_a();


ea

wr e

por s value=input_A();

output_A(value);

output_high(pin);//setanoutputtologic1

output_low(pin);//setanoutputtologic0

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PIC16 C Program Basics Variables Looping

2.2 PIC16 C Program Basics

Decisions

The purpose of an embedded program is to read in data or control inputs, to process them and operate the outputs as required.

The program for processing the data usually contains repetitive loops


,value.

15

Variables

Variables:

isalabelattachedtothememorylocationwherethevariablevalueisstored.

automat ca yass gne tot enextava a e ocat onor ocat ons manyvariabletypesneedmorethan1byteofmemory).

mustbedeclaredatthestartoftheprogramblock,sothatthecompilercanallocateacorrespondingsetoflocations.

Onlyalphanumericcharacters(az,AZ,09)canbeusedforvariablenames

Variablevalues


indecimalbydefault

inhexadecimalwiththeprefix0x,forexample,0xFF

Bydefault,theCCScompilerisnotcasesensitive,

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Listing 2.2 Variables

/ * Sour ce code f i l e: VARI . CAut hor , dat e, ver si on: MPB 11- 7- 07 V1. 0Pr ogr am f unct i on: Out put s an 8- bi t var i abl e

.*******************************************************/

#i ncl ude "16F877A. h"

voi d mai n( ){

i nt x; / / Decl ar e var i abl e and t ype


x=99; / / Assi gn var i abl e val ueout put _D( x) ; / / Di spl ay t he val ue i n bi nar y

}

17

Looping Mostrealtimeapplicationsneedtoexecutecontinuouslyuntiltheprocessoristurnedofforreset.

InCthiscanbeimplementedasawhileloop,asinListing2.3.

/ * Sour ce code f i l e: ENDLESS. CAut hor , dat e, ver si on: MPB 11- 7- 07 V1. 0Pr ogr am f unct i on: Out put s var i abl e countSi mul at i on ci r cui t : OUTBYTE. DSN

*******************************************************/#i ncl ude "16F877A. hvoi d mai n( ){


whi l e( 1) / / Loop endl essl y{ out put _D( x) ; / / Di spl ay val ue

x++; / / I ncr ement val ue}

}

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DecisionMaking

Thesimplestwaytoillustratebasicdecisionmakingistochangeanoutputdependingonthestateofaninput.

Figure2.4 showtestcircuitwithinputswitch

The effect of the programis to switch on the output if

the input is high.

The switch needs to beclosed before running to


see this effect.

The LED cannot be

switched off again until theprogram is restarted.

19

Listing 2.4 IF statement

/ * Sour ce code f i l e: I FI N. CAut hor , dat e, ver si on: MPB 11- 7- 07 V1. 0Pr ogr am f unct i on: Test s an i nputSi mu at i on ci rcui t : I NBI T. DSN

*******************************************************/#i ncl ude "16F877A. h"

voi d mai n( ){

i nt x; / / Decl ar e t est var .out put _D( 0) ; / / Cl ear al l out put s


whi l e( 1) / / Loop al ways{

x = i nput ( PI N_C0) ; / / Get i nputi f ( x==1) out put _hi gh( PI N_D0) ; / / Change out

}}

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LoopControl

Theprogramcanbesimplifiedbycombiningtheinputfunctionwiththeconditionstatementasfollows:

if (input(PIN_C0)) output_high(PIN_D0);

Theconditionalsequencecanalsobeselectedbyawhilecondition.

InProgramWHILOOP.C(Listing2.5) theinputistestedintheloopconditionstatementandtheoutputflashedon

andoffwhiletheswitchis open(inputhigh).

Iftheswitchisclosed,theflashloopisnotexecutedandtheLEDisswitchedoff.


Listing 2.5 Conditional loop/ * Sour ce code f i l e: WHI LOOP. C

Aut hor, date, versi on: MPB 11- 7- 07 V1. 0Pr ogr am f unct i on: I nput cont rol s out put l oopSi mul at i on ci r cui t : I NBI T. DSN

*******************************************************/#i ncl ude "16F877A. h"#use del ay ( cl ock=1000000) / / MCU cl ock = 1MHzvoi d mai n( ) {

whi l e( 1){

whi l e( i nput ( PI N_C0) ) ; / / Repeat whi l e swi t ch open{ output_ hi gh( PI N_D0) ;


e ay_ms ; e ay . sout put_ l ow( PI N_D0) ;del ay_ms( 500) ; / / Del ay 0. 5s

}output_ l ow(P I N_D0) ; / / Swi tch of f LED

}}

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FORLoop

TheWHILElooprepeatsuntilsomeexternaleventorinternallymodifiedvaluesatisfiesthetestcondition.

Inothercases weneedaloo tore eatafixednumberoftimes.

TheFORloopusesaloopcontrolvariable,whichissettoaninitialvalueandmodifiedforeachiterationwhileadefined

conditionistrue.

InthedemoprogramFORLOOP.C(Listing2.6),theloopcontrol


keyword.

23

FORLoop


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SIRENProgram

AprogramcombiningsomeofthesebasicfeaturesisshowninSIREN.C(Listing2.7).

,operatingatahigherfrequency.

Theoutputisgeneratedwhentheswitchisclosed(inputC0low).

Thedelaypicksuptheincrementingvalueofstepgivingalongerpulseeachtimetheforloopisexecuted.


T scausesa ursto 255pu seso ncreas ng engt re uc ngfrequency),repeatingwhiletheinputison.

Notethat255isthemaximumvalueallowedforstep,asitisan8bitvariable.

25

Listing 2.7 Siren Program

/ * Sour ce code f i l e: SI REN. CAut hor , dat e, ver s i on: MPB 11- 7- 07 V1. 0Pr ogr am f unct i on: Out put s a si r en soundSi mul at i on ci rcui t : I NBI T. DSN

*******************************************************/#i ncl ude "16F877A. h"#use del ay (cl ock=1000000)voi d mai n(){i nt st ep;

whi l e(1){

whi l e( ! i nput ( PI N_C0) ) / / l oop whi l e swi t ch ON{

fo r ( s tep=0; s tep

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Listing 2.8 Program Blank

/ * Sour ce Code Fi l ename:Aut hor / Dat e/ Ver si on:Progr am Descri pt i on:Hardware/ si mul ati on:

************************************************************/

#i ncl ude " 16F877A. h" / / Speci f y PI C MCU#use / / I ncl ude l i br ar y r out i nes

voi d mai n( ) / / St ar t mai n bl ock{

i nt / / Decl ar e gl obal var i abl es


whi l e( 1) / / St ar t cont r ol l oop{

/ / Progr am st atement s}

} / / End mai n bl ock

27

BlankProgram

AblankprogramisshowninListing2.8,whichcouldbeusedasageneraltemplate.

Weshouldtr tobeconsistentintheheadercommentinformation,soastandardcommentblockissuggested.

Compilerdirectivesareprecededbyhashmarksandplacedbeforethemainblock.

Otherinitializationstatementsshouldprecedethestartofthemaincontrolloop.Inclusionoftheunconditionalloopoption


reset.

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Table 2.1 A basic set of CCS C components

Compiler Directives#i ncl ude source files Include another source code or header file#use functions(parameters) Include library functions

C Blocks

mai n( condition) {st at ement s } Main program blockwhi l e( condition) {st at ement s } Conditional loopi f ( condition) {st at ement s } Conditional sequencefo r ( condition) {st at ement s } Preset loop

C Functions


del ay_ms( nnn) Delay in millisecondsdel ay_us( nnn) Delay in microseconds

out put _x( n) Output 8-bit code at Port Xout put_ hi gh( PI N_nn) Set output bit highout put_ l ow( PI N_nn) Set output bit lowi nput ( PI N_nn) Get input

29

Variable types

2.3 PIC16 C Data Operations

oa ng po n num ers CharactersAssignment operators

A main function of any computer program is to carry out calculationsand other forms of data processing. Data structures are made up ofdifferent types of numerical and character variables, and a range ofarithmetical and lo ical o erations are needed.


Microcontroller programs do not generally need to process largevolumes of data, but processing speed is often important.

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Table 2.1 Integer Variables

Name Type Min Max

i nt 1 1 bit 0 1

unsi gned i nt 8 8 bits 0 255

si gned i nt 8 8 bits -127 +127


si gned i nt 16 16 bits -32767 +32767



si gned i nt 32 32 bits -2147483647 +2147483647

31

Table 2.2 Microchip/CCS Floating Point Number Format

Exponent Sign Mantissa

xxxx xxxx x xxx xxxx xxxx xxxx xxxx xxxx

FloatingPointNumberFormat

8 bits 1 23 bits

Table 2.4 Example of 32-bit floating point number conversion

FP number : 1000 0011 1101 0010 0000 0000 00000000


Mant i ssa: 101 0010 0000 0000 00000000

Exponent : 1000 0011

Si gn: 1 = negat i ve number

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Operation Symbol EXAMPLE

Equal to == i f ( a == 0) b=b+5;

Table2.7:ConditionalOperators

Not equal to != i f ( a != 1) b=b+4;

Greater than > i f ( a > 2) b=b+3;

Less than < i f ( a < 3) b=b+2;

Greater than or equal to >= i f ( a >= 4) b=b+1;


ess an or equa o

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2

While Loops

The basic while(condition) provides a logical test at the start ofa loop, and the statement block is executed only if thecondition is true. It may, however, be desirable that the loop

oc e execu e a eas once, par cu ar y e escondition is affected within the loop. This option is provided bythe do..while(condition) syntax. The difference between thesealternatives is illustrated in Figure 2.7 . The WHILE test occursbefore the block and the DO WHILE after.


.same block of statements contained within both types of loop.

The WHILE block is not executed because the loop controlvariable has been set to 0 and is never modified. By contrast, count is incremented within the DO WHILE loop before beingtested, and the loop therefore is executed.

Figure2.3.1ComparisonofWhileandDo..WhileLoop

on o

n True?

Statement

Block Conditio

n True?

Statement

Block


(a) While loop (b) Do..While loop

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2

/ / DOWHI LE. C

/ / Compar i son of WHI LE and DO WHI LE l oops#i ncl ude "16F877A. Hmai n( ){

Listing2.9DOWHILE.Ccontainsbothtypesofwhileloop

i nt out byte1=0;i nt out byte2=0;i nt count ;count =0; / / Thi s l oop i s not

whi l e ( count ! =0) / / execut ed{ out put _C( out byt e1) ;

out byt e1++;count - - ;}


count =0; hi s l oop i sdo / / execut ed{ out put _C( out byt e2) ;

out byt e2++;count - - ;} whi l e ( count! =0);whi l e(1) {};

}

Break, Continue, and Goto

It may sometimes be necessary to break the execution of a loop orblock in the middle of its sequence ( Figure 2.8 ). The block must be

,the block (continue) or proceeding to the next one (break).

Occasionally, an unconditional jump may be needed, but this shouldbe regarded as a last resort, as it tends to threaten the programstability. It is achieved by assigning a label to the jump destination andexecuting a goto..label.


The use of these control statements is illustrated in Listing 2.10 . Theevents that trigger break and continue are asynchronous (independentof the program timing) inputs from external switches, which allows thecounting loop to be quit or restarted at any time.

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2

label

Figure2.8Break,continueandgoto

Statement

Block

ContinueGoto

Break


/ / CONTI NUE. C/ / Cont i nue, br eak and got o j umps#i ncl ude "16F877A. H"#use del ay( cl ock=4000000)

Listing2.10 Continue,Break&Goto

ma n{

i nt outbyte;agai n: out byt e=0; / / Got o dest i nat i onwhi l e( 1){

out put _C( out byt e) ; / / Loop oper at i ondel ay_ms( 10) ;


i f ( ! i nput ( PI N_D0) ) cont i nue; / / Restar t l oopi f ( ! i nput ( PI N_D1) ) br eak; / / Ter mi nat e l oopdel ay_ms( 100) ;i f ( out byt e==100) got o agai n; / / Uncondi t i onal j ump

}}

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2

Listing 2.11 Comparison of Switch and If..Else control/ / SWI TCH. C/ / Swi t ch and i f . . el se sequence cont r ol/ / Same r esul t f r om bot h sequences#i ncl ude "16F877A. h

voi d mai n(){

i nt8 i nbi ts ;whi l e(1)

i nbi ts = i nput _D( ) ; / / Read i nput byt e/ / Swi t ch. . case opt i on. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

swi t ch( i nbi t s) / / Test i nput byt e{

case 1: out put _C( 1) ; / / I nput = 0x01, out put = 0x01br eak; / / Qui t bl ock



def aul t : out put _C( 0) ; / / I f none of t hese, out put = 0x00}

/ / I f . . el s e opt i on. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .i f ( i nput ( PI N_D0) ) out put _C( 1) ; / / I nput RD0 hi ghi f ( i nput ( PI N_D1) ) out put _C( 2) ; / / I nput RD1 hi ghi f ( i nput( PI N_D0) && i nput( PI N_D1)) output_C(7); / / Both hi ghel se out put _C( 0) ; / / I f none of t hese, out put = 0x00

}}

ClassAssignments1. WriteaCfunctiontoconvertaBCDcodetoa

commonanode7segmentLEDcode

. ,

thenadd5tothemandoutputtheresulttoPortD.

3. WriteaCstatementtoconvertnumbers0to9to

theirASCIIhexcode.

4. Writeafunctiontodetectabuttonpressand


5. WriteaCprogramtocreateachasingLEDeffect

with8singleLEDsatportD.

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2

2.5PIC16CFunctionsandStructure

ProgramstructureFunctions,arguments

Globalandlocalvariables

ThestructureofaCprogramiscreatedusingfunctions(Figure2.11).Thisisablockofcodewrittenandexecutedasaselfcontainedprocess,receiving

therequiredparameters(datatobeprocessed)fromthecallingfunction

andreturningresultstoit.Main()istheprimaryfunctioninallCprograms,

withinwhichtherestoftheprogramisconstructed.


WhenrunningonaPC,main()iscalledbytheoperatingsystem,andcontrolisreturnedtotheOSwhentheCprogramisterminated.Inthe

microcontroller,main()issimplyusedtoindicatethestartofthemaincontrolsequence,andmorecareneedstobetakeninterminatingthe

program.

Normally,theprogramrunsinacontinuousloop,butifnot,thefinal

void fun1()

LEVEL 0 LEVEL 1 LEVEL 2

Figure2.11HierarchicalCprogramstructure

Main(){

statementsfun1()statementsstatements............

statements......

}

void fun2(arg){

void fun3{


....statementsfun2(arg)statements

}

statements...fun3...return(val)

}

statements......

}

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2

BasicFunctions AsimpleprogramusingafunctionisshowninFUNC1.C,Listing2.12.The

mainblockisveryshort,consistingofthefunctioncallout()andawhile

statement,whichprovidesthewaitstateattheendofmain().

n scase, evar a esare ec are e ore ema n oc . sma esthemglobalinscope;thatis,theyarerecognizedthroughoutthewhole

programandwithinallfunctionblocks.Thefunctionout()isalsodefined

beforemain(),sothat,whenitiscalled,thefunctionnameisrecognized.The

functionstartswiththekeywordvoid,whichindicatesthatnovalueis

returnedbythefunction.Thesignificanceofthisisexplainedshortly.

ThefunctionitselfsimplyincrementsPortCfrom0to255.Itcontainsafor


oop oprov ea e ay,so a eou pu coun sv s e. s sas mp e

alternativetothebuiltindelayfunctionsseeninpreviousexamplesandis

usedheretoavoidtheinclusionofsuchfunctionswhilewestudyuserdefinedfunctions.Itsimplycountsuptoapresetvaluetowastetime.The

delaytimeiscontrolledbythissetvalue.

/ / FUNC1. C/ / Functi on cal l str ucture#i ncl ude "16F877A. Hi nt8 out byt e=1;

Listing2.12 Basicfunctioncall

i nt 16 n;voi d out ( ) / / St ar t of f unct i on bl ock{

whi l e ( out byt e! =0) / / St ar t l oop, qui t when out put =0{

out put _C( out byte) ; / / Out put code 1 0xFFout byt e++; / / I ncr ement out putf or ( n=1; n

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2

GlobalandLocalVariables

Now,assumethatwewishtopassavaluetothefunctionforlocal.Thesimplestwayistodefineitasaglobalvariable,whichmakesitavailable

throughouttheprogram.InprogramFUNC2.C,Listing2.13,thevariable

coun , o ng e e aycoun , ence e e ay me, sg o a .

Ifthereisnosignificantrestrictiononprogrammemory,globalvariablesmaybeused.However,microcontrollers, bydefinition,havelimited

memory,soitisdesirabletouselocalvariableswheneverpossiblewithin

theuserfunctions.Thisisbecauselocalvariablesexistonlyduringfunction

execution,andthelocationsusedforthemarefreeduponcompletionof

functioncall.ThiscanbeconfirmedbywatchingthevaluesofCprogram


var a esw en eprogram sexecu e ns mu a onmo e e oca

onesbecomeundefinedoncetherelevantfunctionblockisterminated.

Ifonlyglobalvariablesareusedandthefunctionsdonotreturnresultstothecallingblock,theybecomeprocedures.ProgramFUNC3.C,Listing2.14,

showshowlocalvariablesareused.

/ / FUNC2. C#i ncl ude "16F877A. Hi nt 8 out byte=1; / / Decl ar e gl obal var i abl esi nt 16 n, count ;

Listing2.13Passingaparametertothefunction

voi d out ( ) / / Funct i on bl ock{

whi l e ( out byt e!=0){ out put _C( out byt e) ;

out byt e++;f or ( n=1; n

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2

/ / FUNC3. C

/ / Use of l ocal vari abl es

#i ncl ude " 16F877A. H"

i nt 8 out b t e=1 Decl ar e l obal var i abl es

Listing2.14 Localvariables

i nt 16 count ;

i nt out ( i nt 16 t ) / / Decl ar e ar gument t ypes{

i nt 16 n; / / Decl ar e l ocal var i abl e

whi l e ( i nput( PI N_D0)) / / Run output a t speed t{ out byt e++;

f or ( n=1; n

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2

Include and use directives Header file listing and directives

2.8PIC16CCompilerDirectives

Compiler directives are typically used at the top of the program to setup compiler options, control project components, define constantlabels, and so on before the main program is created. They arepreceded by the hash symbol to distinguish them from othertypes of statements and do not have a semicolon to end the line.


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3.TimerandInterrupt Interrupt: Interruptsallowanexternaleventto

initiateacontrolsequencethattakes

.

Theinterruptserviceroutine(ISR)carriesoutsomeoperationassociated

withtheportorinternaldevicethat

requestedtheinterrupt.


hardwaretimers,whichprovidedelays,timedintervalsandmeasurement.

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3

3.TimerandInterrupt

PIC16F877has14interruptsourcesNo InterruptLabel InterruptSource

1 INT_EXT ExternalinterruptdetectonRB0

2 INT_RB ChangeonPortBdetect

3 INT_TIMER0

(INT_RTCC)

Timer0overflow

4 INT_TIMER1 Timer1overflow


_

6 INT_CCP1 Timer1captureorcomparedetect

7 INT_CCP2 Timer2captureorcomparedetect

3.TimerandInterrupt PIC16F877has14interruptsources

No InterruptLabel InterruptSource

8 INT_TBE USARTtransmitdatadone

9 INT_RDA USARTreceivedataready

10 INT_SSP SerialdatareceivedatSPIorI2C

11 INT_BUSCOL I2Ccollisiondetected

12 INT_PSP Datareadyatparallelserialport


13 INT_AD Analogtodigitalconvertercomplete

14 INT_EEPROM EEPROMwritecompletion

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3

CInterrupts

CCSCInterruptFunctions


InterruptexampleOSC1/CLKIN

13

OSC2/CLKOUT14

RB3/PGM 36

RB2 35

RB1 34

RB0/INT 33

MCLR/Vpp/THV1

U1

R110k

X1

4MHzC1

15pF

RA0/AN0

RA1/AN13

RA2/AN2/VREF-4

RA4/T0CKI6

RA5/AN4/SS7

RE0/AN5/RD8

RE1/AN6/WR9

RE2/AN7/CS10

RC1/T1OSI/CCP2 16

RC2/CCP1 17

RC3/SCK/SCL 18

19

RB7/PGD 40

RB6/PGC 39

RB5 38

RB4

RC7/RX/DT 26

RC6/TX/CK 25

RC5/SDO 24

RC4/SDI/SDA 23

RA3/AN3/VREF+5

RC0/T1OSO/T1CKI 15

1 20

U29

RP1

C2

15pF


RD1/PSP1 20

RD7/PSP7 30

RD6/PSP6 29

RD5/PSP5 28

RD4/PSP4 27

RD3/PSP3 22

RD2/PSP2 21

PIC16F877

23

4

5

6

7

8

1918

17

16

15

14

13

9

10

12

11

2

3

4

5

6

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1

220R

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Interruptexample

#include"16F877A.h"#usedelay(clock=4000000)

#int_ext //Interruptname

output_D(255); //ISRaction

delay_ms(1000);

}

voidmain() {

int x;

enable_interrupts(int_ext); //Enablenamedinterrupt

enable_interrupts(global); //Enableallinterrupts


ext_int_edge(H_TO_L); //Interruptsignalpolarity

while(1){ //Foregroundloop

output_D(x);x++;delay_ms(100);

}

}

Interruptstatements #int_xxx

Tellsthecompilerthatthecodeimmediatelyfollowingis

Theinterruptnameisprecededby #(hash)tomarkthestartoftheISRdefinitionandtodifferentiateitfroma

standardfunctionblock.

Aninterruptnameisdefinedforeachinterruptsource.

enable_interrupts(int_ext);


Enablesthenamedinterruptbyloadingthenecessarycodesintotheinterruptcontrolregisters

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Interruptstatements

enable_interrupts(level); Enablestheinterruptatthegivenlevel.

enable_interrupts(GLOBAL);

enable_interrupts(INT_TIMER0);

enable_interrupts(INT_TIMER1);

Disable_interrupts(level) Disableinterruptatthegivenlevel


ext_int_edge(H_TO_L);

Enablestheedgeonwhichtheedgeinterruptshouldtrigger.Thiscanbeeitherrisingorfallingedge.

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ClassAssignment1. WriteCcodetoenableanexternalinterrupt

atRB0withthetriggerlowtohigh

2. WriteaCprogramtocontrol4outputpins

RC0RC3from4inputpinsRB4RB7using

portinterrupt.


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3.PIC16HardwareTimers

ThePIC16F877hasthreehardwaretimersbuiltin:

Timer0:8 it,origina yca e RTCC,t ereatimecounterclock

Timer1:16bit

Timer2:8bit

The rinci almodesofo eration


Countersforexternalevents

Timersusingtheinternalclock.

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Counter/TimerOperation Acounter/timerregisterconsistsofasetofbistablestages

(flipflops)connectedincascade(8,16,or32bits).


An8bitcountercountsupfrom0x00to0xFF

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Flag is set to 1 when overflow (7 to 0)

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Counter/TimerOperation

Timer0isan8bitregisterthatcancountpulsesatRA4;forthispurpose,theinputiscalledT0CKI(Timer0clockinput).

, connectedtoRC0(T1CKI).

Thecountcanberecordedatanychosenpointintime;alternatively,aninterruptcanbegeneratedonoverflowtonotify

theprocessorthatthemaximumcounthasbeenexceeded.

Iftheregisterispreloadedwithasuitablevalue,theinterrupt


.

Timer0hasaprescalerthatdividesbyupto128;

Timer1hasonethatdividesby2,4,or8;

Timer2hasaprescalerandpostscalerthatdividebyupto16.

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TimerFunctionsFunctions Description Examples

Setup_timer_x Setuptimer set_timer_0(RTCC_INTERN

AL|RTCC_DIV_8);

Set_timerx(value) Setthevalueofthe

timer

Set_timer0(81);

Get_timerx() Getthevalueofthe

timer

int x=get_timer0();

Setup_ccpx(mode) SetPWM,capture, or

com are mode

setup_ccp1(ccp_pwm);


Set_pwmx_duty(value) SetPWMdutycycle set+_pwm1_duty(512);

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TimerFunctions

Set_timer_0(mode) RTCC_INTERNAL,RTCC_EXT_L_TO_HorRTCC_EXT_H_TO_L

RTCC_DIV_2,RTCC_DIV_4,RTCC_DIV_8,RTCC_DIV_16,RTCC_DIV_32,RTCC_DIV_64, RTCC_DIV_128,RTCC_DIV_256

Set_timer_1(mode)

T1_DISABLED, T1_INTERNAL,T1_EXTERNAL,T1_EXTERNAL_SYNC

T1_CLK_OUT

T1_DIV_BY_1,T1_DIV_BY_2, T1_DIV_BY_4, T1_DIV_BY_8

Example:


set_timer_0(RTCC_INTERNAL|RTCC_DIV_8)

setup_timer_1(T1_DISABLED);//disablestimer1

setup_timer_1(T1_INTERNAL|T1_DIV_BY_4);

setup_timer_1(T1_INTERNAL|T1_DIV_BY_8);

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TimerFunctions setup_timer_2

(mode,

period,

postscale)

modemaybeoneofT2_DISABLED,T2_DIV_BY_1,_ _ _ , _ _ _

periodisaint 0255thatdetermineswhentheclockvalueisreset,

postscaleisanumber116thatdetermineshowmanytimeroverflowsbeforeaninterrupt:(1


meansonce, means w ce,an soon .

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TimerFunctions

CreatedelaybytimersN=2n (T*Fclock)/(4*Prescaler)

N:thecountnumber

n:bitnumberoftimer(Timer0&2:n=8,Timer1:

n=16)

T:delaytime

Fclock:frequencyofcrystal


Prescaler:prescaler number

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The program that carries outthe function of a countingcircuit counts from 00 to 19and displays on two 7-segleds connected to port C

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PWMmode

InPulseWidthModulationmode,aCCPmodulecanbeusedtogenerateatimedoutputsignal.

adjustablehigh(mark)period.

CCSCfunctions:

Set_pwm1_duty(value);

Set_pwm2_duty(value);

*


PR2isthecountvalueoftimer2

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PWMmodeExample#include"16F877A.h"

voidmain()

setup_ccp1(ccp_pwm); //Selecttimerandmode

set_pwm1_duty(500); //Setontime

setup_timer_2(T2_DIV_BY_16,248,1);//Clockrate&output

//period

while(1){} //Waituntilreset


}

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Produce an output at CCP1 of 250Hz (4ms) and a mark-space ratio of 50%with a 4-MHz MCU clock. Explain?

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CompareMode

GenerateatimedoutputinconjunctionwithTimer1. The16bitCCPRregisterispreloadedwithasetvalue,whichis

.

matchestheCCPRvalue,theoutputpintogglesandaCCP

interruptisgenerated.Ifthisoperationisrepeated,aninterrupt

andoutputchangewithaknownperiodcanbeobtained.


Capturemode TheCCPpinissettoinputandmonitoredforachangeofstate. Whenarisingorfallingedge(selectable)isdetected,thetimer

registerisclearedto0andstartscountingattheinternalclock

rate.

Whenthenextactiveedgeisdetectedattheinput,thetimerregistervalueiscopiedtotheCCPregister.Thecounttherefore

correspondstotheperiodoftheinputsignal.Witha1MHz

instructionclock,thecountisinmicroseconds


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Exercise TimerInterrupt

1) Calculate thefrequency of the pulseon PIN B0 created by

right figure, given thatFOSC = 4MHz

2) Write the program thatcreate a 2Hz ulse on


PIN_B1, given thatFOSC = 4MHz and

dutycycle = 20%

ClassAssignment1. WriteaprogramforPIC16F877tocreate

rectanglepulses2KHzatRB1usinginterrupt

mer .

2. WriteaCprogramforPIC16F877tocreate

rectanglepulses0.5KHzand1KHzatRC0and

RC1withdutycycle50%.UseTimer1interrupt

with4MHzOSC.

B K Th t i T HBK

3. Writetheprogramthatcreatea2Hzpulseon

PIN_B1,giventhatFOSC=4MHzanddutycycle

=20%

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Documents

ESD-Ch5_new