4) PIC IO Port Programming

7/27/2019 4) PIC IO Port Programming

1/18

1

PIC I/O Port ProgrammingChapter 3


2/18

2

PIC18F4550 Pin Diagram


3/18

3

I/O Ports on PIC18F4550 Consist of five ports:

PORTA (RAx) 7 Pins

PORTB (RBx) 8 Pins PORTC (RCx) 8 Pins - 3 SFRPORTx.

PORTD (RDx) 8 Pins TRISx, and LATx

PORTE (REx) 3 Pins


4/18

4

TRIS Register (TRIState)All the five ports can be used as either output or input.

If TRISx = 0 ; PORTx = output

If TRISx = 1 ; PORTx = input


5/18

5

Setting up the I/O PortsMOVLWB11110000

MOVWFTRISB;RB7,RB6,RB5,RB4 AS INPUT;RB3,RB2,RB1,RB0 AS OUTPUT

CLRFTRISB;clear all TRISB bits PORTB output

SETFTRISC;set all TRISC bits PORTC input


6/18

6

Writing output bits to I/O PORTCLRFTRISB;set PORTB as output

MOVLW0x55; W=01010101

MOVWFPORTB;PORTB = 01010101


7/187

Reading input bits from I/O

PORTSETFTRISC;set PORTC as input

MOVFPORTC,W;get PORTC & move to W

MOVWFMYREG;MYREG = 01010101


8/188

Study Example 4-1Write a test program for the PIC18 chip to toggle all the bits of PORTB,

PORTC, and PORTD every of a sec. Assume crystal frequency is 4 MHz.#include

R1 equ 0x07

R2 equ 0x08

ORG 0

CLRF TRISB ;make Port B an output port

CLRF TRISC ;make Port C an output port

CLRF TRISD ;make Port D an output port

MOVLW 0X55 ; WREG = 55h

MOVWF PORTB ;put 55H to Port B pins

MOVWF PORTC ;put 55H to Port C pins

MOVWF PORTD ;put 55H to Port D pinsLOOP COMF PORTB, F;toggle bits of Port B

COMF PORTC, F ;toggle bits of Port C

COMF PORTD, F ;toggle bits of Port D

CALL DELAY

BRA LOOP


9/189

QDELAY

MOVLWD 200

MOVWFR1

D1 MOVLWD 250MOVWFR1

D2 NOP

NOP

DECF R2, FBNZD2

DECFR1

BNZD1

RETURN

END

Inst Cycle Duration = 4/fosc = 1 Sec

Delay = 250 X 200 X


10/1810

I/O Bit Manipulation


11/1811

BIT-ORIENTED OPERATIONS1. Some times, we are interested to access only 1 or 2 bits of the port insteadof the entire 8 bits.2. BIT Oriented operation are supporting to do the above things in PIC18


12/18

12

BSF(bit set fileReg)

BCF(bit clear fileReg)Syntex:

BSFfileReg, bit_numBCFfileReg, bit_num

Example:

BSFPORTD,2;Set bit RD2

BCFPORTD,5;Clear bit RD5


13/18

13

Study Example:

CLRFTRISD;Make PORT D an output

BSFPORTD, 0 ; Bit set turns on RD 0CALL DELAY

BSF PORTD,1 ; Bit set turns on RD 1

CALL DELAY

-----------------------------------------------------------------------------------------

BCFTRISB, 2 ;bit = 0, make RB2 an output pinAGAIN BSFPORTB,2 ; bit set (RB2 = high)

CALL DELAY

BCFPORTB, 2 ; bit clear (RB2=low)

CALL DELAY

BRA AGAIN

An LED is connected to each pin of PORT D. Write a program to turn oneach LED from pin D0 to pin D7. Call a delay module before turning on the

next LED


14/18

14

Exercise 1Write a program to generate 1kHz square wave with80% duty cycle on bit3 of PORTC. Prepare theflowchart.


15/18

15

BTFSS(bit test fileReg, skip if set)

BTFSC(bit test fileReg, skip if clear)

In order to make a decision on based on the status of a

given bit in the file register, we use the followinginstructions.

BTFSS - to monitor the status of single bit HIGH

BTFSC to monitor the status of single bit LOW


16/18

16

Example 4-4Write a program to perform the following:

a)Keep monitoring the RB2 bit until it becomes HIGH

b)When RB2 becomes HIGH, write value 45H toPORTC, and also send a HIGH-to-LOW pulse to RD3


17/18

17

Example 4-4 (Solution)BSF TRISB,2; RB2 as inputCLRFTRISC ; PORT C as output BCF PORTD,3 ; RD3 as output

MOVLW0x45; WREG = 45h

AGAINBTFSS PORTB,2 ; bit test RB2 for HIGH

BRAAGAIN; Keep checking LOW

MOVWFPORTC; issue WREG to Port C

BSF PORTD,3; bit set file reg RD3 (H-L)

BCFPORTD,3 ; bit clear file reg RD3 (L)


18/18

18

Example 4-5

BSF TRISB,3BCF TRISC,5

HERE BTFSC PORTB,3

BRA HERE

BSF PORTC,5

BCF PORTC,5BRA HERE

Assume RB3 is an input. If it goes LOW, it means that the door open.

Monitor the bit continuously. Whenever it goes LOW, sent a HIGH-to-LOW

pulse to port RC5.

4) PIC IO Port Programming

Documents

Transcript of 4) PIC IO Port Programming