chapter 4 pic io programming

8/19/2019 Chapter 4 PIC IO Programming

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Chapter 4Chapter 4

PIC18 I/O ProgrammingPIC18 I/O Programming

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PIC18 Parallel PortsPIC18 Parallel Ports

• I/O ports are available in PIC18 toI/O ports are available in PIC18 tointeract, monitor and controlinteract, monitor and control

peripherals.peripherals.

LEDLED !"egment LED!"egment LED2


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• #he n$mber o% ports in the PIC18 %amilhe n$mber o% ports in the PIC18 %amil&

depends on the n$mber o% pins on thedepends on the n$mber o% pins on the

chip.chip.

• PIC18'4()* has %ive ports+ Port !EPIC18'4()* has %ive ports+ Port !E

• Di%%erent ports have di%%erent n$mber o%Di%%erent ports have di%%erent n$mber o%

pins+pins+

– Port , -, C and D+ 8 pinsPort , -, C and D+ 8 pins

– Port E+ pinsPort E+ pins

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• #he behavio$r o% each port is controlled#he behavio$r o% each port is controlled

b& to special %$nction registers 0"'s2+b& to special %$nction registers 0"'s2+

– PO#3 indicates the voltage levels on thePO#3 indicates the voltage levels on the

pins o% the devicepins o% the device – #I"3 data direction register #I"3 data direction register

• e.g., 'or Port -, e have PO#- ande.g., 'or Port -, e have PO#- and

#I"-#I"-

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#I"3 and PO#3 "'s#I"3 and PO#3 "'s

• Each o% the Ports !E can be $sed %orEach o% the Ports !E can be $sed %or

inp$t and o$tp$t.inp$t and o$tp$t.

• #I"3 "' is $sed %or designating the#I"3 "' is $sed %or designating the

direction o% a portdirection o% a port – * %or o$tp$t 0e.g., Controlling LED state2* %or o$tp$t 0e.g., Controlling LED state2

– 1 %or inp$t 0e.g., 5e& scan21 %or inp$t 0e.g., 5e& scan2

• e.g., #o o$tp$t data to Port -+e.g., #o o$tp$t data to Port -+ – 6rite *s to #I"- "'6rite *s to #I"- "'

– 6rite data to PO#- "'6rite data to PO#- "'

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#I"3 and PO#3 "'s#I"3 and PO#3 "'s

• e.g., o$tp$t the he3 val$e *3)7 to Port Ce.g., o$tp$t the he3 val$e *3)7 to Port C

clrf TRISCclrf TRISC

movlw 0x26 movlw 0x26

movwf PORTC movwf PORTC

• e.g., ead the c$rrent val$e o% Port De.g., ead the c$rrent val$e o% Port D

into 6E register into 6E register setf TRISDsetf TRISD

movf PORTD, W movf PORTD, W

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I/O ports and bit!addressabilit&I/O ports and bit!addressabilit&

• O%ten need to access individ$al bit o% theO%ten need to access individ$al bit o% theport instead o% the entire 8 bits.port instead o% the entire 8 bits.

• PIC18 provides instr$ctions that alterPIC18 provides instr$ctions that alterindivid$al bits itho$t altering the rest o%individ$al bits itho$t altering the rest o%the bits in the port.the bits in the port.

• 9ost common bit!oriented instr$ctions+9ost common bit!oriented instr$ctions+

Instr$ctionsInstr$ctions '$nction'$nction

bs% %ileeg, bitbs% %ileeg, bit -it "et %ileeg-it "et %ileegbc% %ileeg, bitbc% %ileeg, bit -it Clear %ileeg-it Clear %ileeg

btg %ileeg, bitbtg %ileeg, bit -it #oggle %ileeg-it #oggle %ileeg

bt%sc %ileeg, bitbt%sc %ileeg, bit -it test %ileeg, s:ip i% clear -it test %ileeg, s:ip i% clear

bt%ss %ileeg, bitbt%ss %ileeg, bit -it test %ileeg, s:ip i% set-it test %ileeg, s:ip i% set7


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bs%, bc% and btgbs%, bc% and btg

• bs% %ileeg, bitbs% %ileeg, bit

– e.g.,e.g., bsf PortB, 5 bsf PortB, 5 sets -it ( o% Port - to besets -it ( o% Port - to be

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• bc% %ileeg, bitbc% %ileeg, bit – e.g.,e.g., bcf PortB, 5 bcf PortB, 5 sets -it ( o% Port - to besets -it ( o% Port - to be

*.*.

• btg %ileeg, bitbtg %ileeg, bit – e.g.,e.g., btg PortB, 5 btg PortB, 5 toggles -it ( o% Port -toggles -it ( o% Port -

0i.e., sets it to 1 i% the c$rrent val$e is * ; vice0i.e., sets it to 1 i% the c$rrent val$e is * ; vice

versa2versa2

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Chec:ing the state o% an I/O portChec:ing the state o% an I/O port

• bt%sc 0bit test %ile, s:ip i% clear2 and bt%ssbt%sc 0bit test %ile, s:ip i% clear2 and bt%ss

0bit test %ile, s:ip i% set2 are $sed to ma:e0bit test %ile, s:ip i% set2 are $sed to ma:e

branching decision based on the stat$sbranching decision based on the stat$s

o% a given bit.o% a given bit.• e.g., bt%sc PO#D, ) s:ips the ne3te.g., bt%sc PO#D, ) s:ips the ne3t

instr$ction i% -it ) o% Port D e


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E3ample+ bt%ssE3ample+ bt%ss

• e.g., 6rite a program to 0a2 :eepe.g., 6rite a program to 0a2 :eep

monitoring -) bit $ntil it becomes highmonitoring -) bit $ntil it becomes high

0b2 6hen -) becomes high, rite 4(=0b2 6hen -) becomes high, rite 4(=

to Port Cto Port C bsf TRISB, 2; set RB2 s !"#$t bsf TRISB, 2; set RB2 s !"#$t

clrf TRISC; set Port C s o$t#$tclrf TRISC; set Port C s o$t#$t

movlw 0x%5 movlw 0x%5

&g!"' btfss PORTB, 2 &g!"' btfss PORTB, 2

br &g!" br &g!"

movwf PORTC movwf PORTC

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E3ample+ bt%ssE3ample+ bt%ss

• e.g., 6rite a program to chec: -).e.g., 6rite a program to chec: -). – I% -) > *, send the letter ?@A to Port DI% -) > *, send the letter ?@A to Port D

– I% -) > 1, send the letter ?BA to Port DI% -) > 1, send the letter ?BA to Port D

bsf TRISB, 2; set RB2 s !"#$t bsf TRISB, 2; set RB2 s !"#$tclrf TRISD; set Port D s o$t#$tclrf TRISD; set Port D s o$t#$t

&g!"' btfss PORTB, 2 &g!"' btfss PORTB, 2

br Over br Over

movlw &()( movlw &()(

movwf PORTD movwf PORTD br &g!" br &g!"

Over' movlw &(*(Over' movlw &(*(

movwf PORTD movwf PORTD

br &g!" br &g!"

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E3ample+ bt%scE3ample+ bt%sc

• e.g., Per%orm the same %$nction $singe.g., Per%orm the same %$nction $sing

bt%scbt%sc

bsf TRISB, 2; set RB2 s !"#$t bsf TRISB, 2; set RB2 s !"#$t

clrf TRISD; set Port D s o$t#$tclrf TRISD; set Port D s o$t#$t &g!"' btfsc PORTB, 2 &g!"' btfsc PORTB, 2

br Over br Over

movlw &+*( movlw &+*(


br &g!" br &g!"

Over' movlw &+)(Over' movlw &+)(


br &g!" br &g!"

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Inter%acing ith LEDInter%acing ith LED

• #o a&s o% connecting LEDs to I/O ports+#o a&s o% connecting LEDs to I/O ports+ – Common CathodeCommon Cathode+ LED cathodes are gro$nded+ LED cathodes are gro$nded

and logic 1 %rom the I/O port t$rns on the LEDs.and logic 1 %rom the I/O port t$rns on the LEDs.

– Common node+ LED anodes are connected to theCommon node+ LED anodes are connected to the

poer s$ppl& and logic * %rom the I/O port t$rns onpoer s$ppl& and logic * %rom the I/O port t$rns onthe LEDs.the LEDs.

Common Cathode

Active high Active low

Common Anode

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Inter%acing ith !"egment LEDInter%acing ith !"egment LED

• O%ten $sed to displa& -CDO%ten $sed to displa& -CDn$mbers 0* thro$gh 2 and an$mbers 0* thro$gh 2 and a

%e alphabets%e alphabets

• gro$p o% eight LEDs gro$p o% eight LEDsph&sicall& mo$nted in theph&sicall& mo$nted in the

shape o% the n$mber eightshape o% the n$mber eight

pl$s a decimal pointpl$s a decimal point

• Each LED is called aEach LED is called asegment and labeled as ?aAsegment and labeled as ?aA

thro$gh ?gA.thro$gh ?gA.

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• In a common cathodeIn a common cathodeseven!segment LEDseven!segment LED – ll cathodes arell cathodes are

connected together toconnected together togro$nd and the anodesgro$nd and the anodesare connected to dataare connected to datalineslines

• Logic 1 t$rns on aLogic 1 t$rns on asegment.segment.

• E3ample+ #o displa&E3ample+ #o displa&digit 1, all segmentsdigit 1, all segmentse3cept b and c sho$lde3cept b and c sho$ldbe o%%.be o%%.

• -&te *****11* > *7 ill-&te *****11* > *7 illdispla& digit 1.displa& digit 1.

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Lab ) #as: 1+ "ingle digit !"egment LEDLab ) #as: 1+ "ingle digit !"egment LED

• #as:+ 6rite a loop to sho digits *! se ** 0n$mber to be displa&ed2 – Instr$ctions to be repeated+ 012 call "@"E 0)2 Displa& digitInstr$ctions to be repeated+ 012 call "@"E 0)2 Displa& digit

pattern stored in 6E 02 call Dela& 042 Increment @$mipattern stored in 6E 02 call Dela& 042 Increment @$mi – #his is an in%inite loop and e do not need to trac: n$mber o%#his is an in%inite loop and e do not need to trac: n$mber o%

repetitionsrepetitions

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Inter%acing ith 4!digit !"egment LEDInter%acing ith 4!digit !"egment LED

• Decoder selects the position here digitDecoder selects the position here digitpattern is displa&ed.pattern is displa&ed.

• Gse time m$ltiple3ing i% e need toGse time m$ltiple3ing i% e need to

displa& all %o$r digits.displa& all %o$r digits.

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Inp$t 1+ Digit PatternInp$t 1+ Digit Pattern

Inp$t )+ 6hich digit &o$Inp$t )+ 6hich digit &o$6ant Inp$t 1 to be6ant Inp$t 1 to be

displa&edHdispla&edH


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Lab ) #as: )+ 4!digit !"egment LEDLab ) #as: )+ 4!digit !"egment LED

#as:+ Displa& &o$r gro$p#as:+ Displa& &o$r gro$pn$mber o% the 4!digit !n$mber o% the 4!digit !segment LED.segment LED.

lgorithmlgorithm

•InitialiFationInitialiFation – 4 %ile registers storing the 4 digits o% &o$r gro$p4 %ile registers storing the 4 digits o% &o$r gro$p

n$mber+ @$m1, @$m), , @$m4n$mber+ @$m1, @$m), , @$m4 – Loc+ 6hich digit the n$mber sho$ld be displa&edHLoc+ 6hich digit the n$mber sho$ld be displa&edH

•Loop+ 'or the %irst digit, get the digit patternLoop+ 'or the %irst digit, get the digit patterncorresponding to J@$m1K b& calling "@"Ecorresponding to J@$m1K b& calling "@"E DigitDigitpattern stored in J6EK. "et Inp$t1 > J6EK andpattern stored in J6EK. "et Inp$t1 > J6EK andInp$t ) > *. Per%orm similar operations %or the second,Inp$t ) > *. Per%orm similar operations %or the second,third and %o$rth digits.third and %o$rth digits.•epeat the loop in%initel&.epeat the loop in%initel&.

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Lab #as: 1+ 8!b$tton :e&padLab #as: 1+ 8!b$tton :e&pad

• Con%ig$ration o%Con%ig$ration o%:e&pad+ P$lled $p:e&pad+ P$lled $p0i.e., 12 hen not0i.e., 12 hen notpressed. * i%pressed. * i%

pressed.pressed.• #as:+ "ho MN#as:+ "ho MN

hen -$tton PMNhen -$tton PMNis pressed. MN>1is pressed. MN>1

to 8to 8

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Lab #as: )+ 434 5e& 9atri3Lab #as: )+ 434 5e& 9atri3

• Con%ig$ration o% :e&Con%ig$ration o% :e&matri3matri3 – Port C connects toPort C connects to

:e&pad matri3:e&pad matri3•

C*! o$tp$ts, C4!C*! o$tp$ts, C4!inp$tsinp$ts

• "ho MN i% -$tton"ho MN i% -$tton5M1N is pressed5M1N is pressedhere MN > * to '.here MN > * to '.

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Program "tr$ct$re %or -oth #as:sProgram "tr$ct$re %or -oth #as:s

• "et I/O direction o% appropriate ports."et I/O direction o% appropriate ports.• call 5e&scancall 5e&scan

– #as: 1+ O$tp$t %rom 1 to , indicating the b$tton#as: 1+ O$tp$t %rom 1 to , indicating the b$ttonthat is pressed. indicates no b$tton is pressed.that is pressed. indicates no b$tton is pressed.

– #as: )+ O$tp$t %rom * to 17, indicating the b$tton#as: )+ O$tp$t %rom * to 17, indicating the b$ttonthat is pressed. * indicates that no b$tton isthat is pressed. * indicates that no b$tton ispressed.pressed.

• call "@"Ecall "@"E – Inp$t+ O$tp$t %rom :e&scanInp$t+ O$tp$t %rom :e&scan

– O$tp$t+ Digit pattern corresponding to inp$t val$eO$tp$t+ Digit pattern corresponding to inp$t val$e – Implemented $sing a loo:$p tableImplemented $sing a loo:$p table

• Port connecting 1!digit !seg LED > O$tp$tPort connecting 1!digit !seg LED > O$tp$t%rom "@"E%rom "@"E

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5e&scan s$bro$tine %or #as: 15e&scan s$bro$tine %or #as: 1

• "can P1 to P8 se


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#as: )+ "canning 434 :e& matri3#as: )+ "canning 434 :e& matri3

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6hen 5( is pressed6hen 5( is pressed

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0

1

1

1

1 1 1 1

0

0

1


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6hen 51( is pressed6hen 51( is pressed

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0

1

1

1

1 1 1 1

0

1

0

0

0


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5e&scan s$bro$tine %or 434 :e& matri35e&scan s$bro$tine %or 434 :e& matri3

1.1.InitialiFe 5EBCODE to *.InitialiFe 5EBCODE to *.).)."et C* to logic * and C1+ to logic 1"et C* to logic * and C1+ to logic 1

..call DetectCol, read the states o% C4+call DetectCol, read the states o% C4+ – *111*111

DetectColO$tp$t > 1DetectColO$tp$t > 1 – 1*111*11

DetectColO$tp$t > )DetectColO$tp$t > )

– 11*111*1 DetectColO$tp$t > DetectColO$tp$t > – 111*111*

DetectColO$tp$t > 4DetectColO$tp$t > 4 – 11111111

@o b$tton is pressed, DetectColO$tp$t > *@o b$tton is pressed, DetectColO$tp$t > *

4.4.#o cases+#o cases+ – I% o$tp$t o% DetectColO$tp$t > *, no b$tton is pressed, scanI% o$tp$t o% DetectColO$tp$t > *, no b$tton is pressed, scan

ne3t ro. dd 4 to 5EBCODE.ne3t ro. dd 4 to 5EBCODE. – I% o$tp$t o% DetectColO$tp$t > *, a b$tton is pressed,I% o$tp$t o% DetectColO$tp$t > *, a b$tton is pressed,

ret$rn 5EBCODE > 5EBCODE DetectColO$tp$tret$rn 5EBCODE > 5EBCODE DetectColO$tp$t

(.(.I% no b$tton is detected to be pressed a%ter scanning %o$rI% no b$tton is detected to be pressed a%ter scanning %o$rros, 5EBCODE > * and e3it the s$bro$tine.ros, 5EBCODE > * and e3it the s$bro$tine.

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Bo$ sho$ld be able to ... Bo$ sho$ld be able to ...

• Code assembl& lang$age to $se theCode assembl& lang$age to $se theports %or inp$t or o$tp$tports %or inp$t or o$tp$t

• Code I/O bit manip$lation programs %orCode I/O bit manip$lation programs %or

the PICthe PIC• Chec: the state o% an I/O port and ma:eChec: the state o% an I/O port and ma:e

branching decision based on itbranching decision based on it

• Inter%ace ith 1!digit/4!digit !segmentInter%ace ith 1!digit/4!digit !segmentLED and :e&pad matri3.LED and :e&pad matri3.

• Bo$ can no start Labs ) and Bo$ can no start Labs ) and

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chapter 4 pic io programming

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