1. I/O Interfacing and Programming
Welcome to . . .
Seminar 5:
I/O Interfacing and Programming
Reprinted with permission of the copyright owner, Microchip Technology Incorporated ©2000, 2001 and All rights reserved. No further reprints or reproductions may be made without Microchip Technology Inc.’s prior written consent.

2. Objectives: At the end of this seminar, you should be able to:
Initialize the input/output ports
Send the data to output ports
Read the data from input ports

3. PIN Diagram of PIC18F4520

4. PIC18F4520 I/O Ports
I/O Ports: Facilitate the microcontroller in communicating with the outside world
5 I/O ports (Port A, B, C, D, E)
36 I/O pins
RE3 is Input only
The rest of the I/O pins are bi-directional
 hence, we need to program the direction of I/O port pins before we use them!

5. PIC18F4520 I/O Ports Port A (8 pins : RA0 – RA7)
Port B (8 pins : RB0 – RB7)
Port C (8 pins : RC0 – RC7)
Port D (8 pins : RD0 – RD7)
Port E (4 pins : RE0 – RE3)
All ports except RE3 can be used for digital I/O . RE3 is input only.
Ports A,B & E can also be used for analog input.

6. Registers Each port has 3 registers associated with it.
TRIS (Data Direction)
PORT (Read/Write DATA from or to I/O pin )
LAT (Data Latch register for read-modify-write)
In order to use a port, we need
-to set the data direction in the TRIS REGISTER
-to read data from/write to the PORT REGISTER

7. PORTx and TRISx
There are five I/O ports in PIC18F They are Ports A, B, C, D and E.
The data registers for these ports are named PORTA, PORTB, PORTC, PORTD and PORTE.
The direction of the individual pins in the port is configured by programming the TRISA, TRISB, TRISC, TRISD and TRISE.
A ‘1’ in the TRISx bit sets the corresponding pin of the port as input whereas a ‘0’ sets the pin as output.

8. Ports A, B & E
I/O pins in Ports A, B and E can either be used as an analog input pin or digital I/O pin.
Indicate their use as analog/ digital pins by writing to the ADCON1 register.

9. ADCON1
Port A, Port B and Port E can be used for digital I/O as well as analog input.
Programming ADCON1 will set Port A , Port B or /and Port E as analog or digital.
A 0x0F to ADCON1 will initialize ALL the pins of Ports A, B and E as digital.
User can also choose to configure some pins as analog while others as digital. For such applications, please refer to the PIC18F4520 Concise Data Book for different binary values to be written to ADCON1.

10. Using I/O Ports Identify the Port to be used
If Port A, B and/or E is used, configure them as digital I/O pins by
Setting ADCON1
Configure the direction of each I/O pin
Using TRISx (E.g Port A use TRISA)
Read from or Write to the pin or port
Using PORTx

11. Example 1
Configure port A such that pins RA<5:4> are inputs and pins RA<3:0> are outputs
Bit <5:4> of TRISA = ‘1’
Bit <3:0> of TRISA = ‘0’
The remaining bits (Bits 6 & 7) can be ‘0’ or ‘1’
Solution:
ADCON1 = 0x0F; // Port A&E as digital I/O
TRISA = 0b ; //RA0-3 as o/p, RA4-5 as i/p

12. Example 2 TRISB = 0b11010110 ; ADCON1 = 0x0f; Solution:
Configure Port B pins 1, 2, 4, 6 and 7 as inputs and pins 0, 3 and 5 as output pins.
Solution:
TRISB = 0b ;
ADCON1 = 0x0f;

13. Example 3 Solution: ADCON1 = 0x0F; // Port A&E as digital I/O
Given the circuit below, configure the directions of the I/O pins used.
RC1
RC0
RC2
RC3
RC4
RC5
RC6
RC7
RA1
RA0
RA2
RA3
RA5
RA4
Solution:
ADCON1 = 0x0F; // Port A&E as digital I/O
TRISA = 0b ; // Port A pin 0-5 are outputs
TRISC = 0b ; //RC0,2,3,6 as o/p, RC1,4,5,7 as i/p

14. Exercise 1
Refer to the schematic diagram shown in the next slide. Write a C program code segment to initialize ALL the input/output ports.

15. Exercise 1 PIC18F4520 Vcc J6 S3 S2 RB0/INT0 RA4 RB1 RB2 RB3 RD3 RD2
R/W RS
VEE
GND
GND1
RA3
RA2
RA1
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
LCD
16 Char X 2 lines RX TX
RC7
RC6
RA0 J9
Piezo Buzzer
RC2

16. Exercise 1 Solution ADCON1 = 0x0F; // Port A, B &E as digital I/O
TRISA = 0b ; //RA1,2 & 3 as o/p, RA0 & 4 as i/p
TRISB = 0b ; // lower 4-bits as o/p
TRISC = 0b ; // RC2 & 6 as o/p, RC7 as i/p
TRISD = 0b ; // lower 4-bits as o/p

17. Project Time!
Let us try to initialize the I/O ports for our Electronic Queueing System

18. Project: Queueing System
Hardware design
PIC18F4520
RB1
16x2 lines
LCD Module
RC0
RC1
RC2
RC3
RC4
RC5
RC6
RC7 D0 D1 D2 D3 D4 D5 D6 D7
RE1
RE2 E RS RW
+5V 5V
RA1
RA0
RA2
+5.0V
RB0
Alarm
Q_request
Button 1
Button 2
Button 3

19. /* Initialise the IO ports */
ADCON1 = 0x0F; /* PORTA, B & E as digital IO */
TRISA = 0xFF; /* PORTA as digital input ports – for buttons*/
TRISB = 0b ; /* RB0 as output pin for alarm */
TRISC = 0x00; /* PORTC as digital output data ports for LCD */
TRISE = 0b ; /* RE1 & RE2 as digital output pin for LCD control */

20. Output Operation
To send data to the whole output port, you can use this instruction:
PORTx = [DATA];
This instruction writes [DATA] to the PORTx
Example: PORTA = 0x0F;

21. Output Operation
To send data to the individual output pins, you can use this instruction:
PORTxbits.Rxn = [DATA];
This instruction writes [DATA] to the PORTx bit n.
Example: PORTCbits.RC4 = 1;

22. Example 4
Write a program segment to configure entire PORTC as output port and write 0x0F to PORTC.
Solution
TRISC = 0b ; // entire Port C as output
PORTC = 0x0F;

23. Example 5 Solution TRISD = 0b11111011; // RD2 as o/p
Assume that a LED is tied to bit 2 of PORT D as shown in the circuit below.
Write a program segment to initialize bit 2 of Port D as output and turn on the LED.
PIC18F4520
RD2 R +V
LED
Solution
TRISD = 0b ; // RD2 as o/p
PORTD = 0x00; // or PORTDbits.RD2 = 0

24. Exercise 2
Given the circuit as shown, write a program segment to turn on LEDs 1, 2 and 6, and turn off LEDs 3, 4 and 5
LED2
RD1
RD2
RD3
RD4
RD5
RD6
PIC18F4520
LED1
LED3
LED4
LED5
LED6
Solution
TRISD = 0b ; // RD1 - 6 as o/p
PORTD = 0b ;

25. Exercise 3
Given the circuit as shown, write a program segment to toggle all the LEDs
LED2
RD1
RD2
RD3
RD4
RD5
RD6
PIC18F4520
LED1
LED3
LED4
LED5
LED6
Solution
TRISD = 0b ; // RD1 - 6 as o/p
PORTD = ~PORTD;

26. Input Operation
The whole input port can be read using the instruction:
A = PORTx;
This instruction reads the contents of PORTx into a register file A
Example: data = PORTB;

27. Input Operation
Individual input pins can be read using the instruction:
A = PORTxbits.Rxn;
This instruction reads the contents of PORTx pin n into a register file A
Example: data = PORTBbits.RB2;

28. Example 6
Write a program segment to configure the entire PORT C as input port and read in the value of PORT C.
Solution
TRISC = 0b ; // entire Port C as input
x = PORTC;

29. Example 7
Refer to the diagram below, write a program segment, to test whether the bit 3 of PORTC is logic 0.
PIC18F4520 +V SW
RC3
Solution
if (PORTCbits.RC3 == 0) {
//continue the task if SW is closed }

30. Exercise 4
An LED is tied to bit 2 of PORT B & the switch SW is connected to bit 3 of PORTB. Write a complete program to:
Initialise Port B
Turn ON or OFF the LED corresponding to switch being CLOSED or OPEN +V
RB2
LED R SW
PIC18F4520
RB3

31. Exercise 4 Solution #include <p18f4520.h> //Directive main() {
/* initialize the I/O port */
ADCON1 = 0x0f; // Port B as digital
TRISB = 0b ; // RB2 as o/p, all other pins as i/p
/* read the input */
if (PORTBbits.RB3 == 0) // if SW is closed, logic ‘0’
PORTBbits.RB2 = 0; // turn ON the LED
else // if SW is open, logic ‘1’
PORTBbits.RB2 = 1; // turn OFF the LED }

32. Exercise 5
Refer to the same schematic diagram as in the Exercise 1. Write a complete C program to toggle all the 4 LEDs in every 0.2S.
Note: Assume that calling the library function Delay10KTCYx(20) will give a delay of 0.2 sec delay.

33. Exercise 5 Solution #include <p18f4520.h> // Directive
#include<delays.h> // include library delay function
void main () { // Function
TRISB = 0b ; // Lower 4 bits of Port B as output
ADCON1 = 0x0f;
PORTB = 0x00; // Initially off all LEDs
while(1) { // Endless loop
PORTB = ~PORTB; // Toggle Port B content
Delay10KTCYx(20); // call library for 0.2sec delay }

34. Summary You have just learnt:
I/O ports of PIC18F4520
Configuring of I/O pin
Reading from and Writing to I/O Pin
I/O Programming
We will learn more programming techniques next week on how to write a looping program.

35. Do-it-yourself Question 1:
Write a ‘C’ program segment to configure all the I/O ports for the circuit shown in next slide.

36. a b d e f c g PIC18F4520 RA4 RA3 RE2 RD7 RD6 RD5 RD4 RD3 RD2 RD1 RC05V
RC0
RC1
+5V M
RC2
RC3
RC4
TIME
SPEED
POWER ON
OFF
RB0
RB1
RB2
RB3
RB4
RB5
RB6
RB7
16x2 lines
LCD Module E RS RW D0 D1 D2 D3 D4 D5 D6 D7
RE0
RE1
Speaker
Motor
HIGH
MID
LOW +V

37. Solution to Question 1: ADCON1 = 0x0F;
TRISA = 0bXX100111; //X can be 1 or 0
TRISB = 0x00;
TRISC = 0b ;
TRISD = 0b ;
TRISE = 0bXXX0X111;
Point out that the X in the binary sequence stands for don’t care condition. Emphasize that students should use either 1 or 0 for these don’t care bits while writing programs.
/*TRISE bit4 must be written as 0 so that PORTD will be in General Purpose I/O mode */

38. Do-it-yourself Question 2:
Write a complete ‘C’ program to initialize the PIC18F4520 to operate the circuit shown below. Continuously, read the switches from RA0 to RA3 and switch on the corresponding LEDs in Port B, for the closed switches. Assume that RB4 to RB7 are not used.
LED3
RB0
RB1
RB2
RB3
PIC18F4520
LED4
LED2
LED1 V+
RA2
RA0 RA1
RA3

39. Solution to Question 2: #include <p18f4520.h> // Directive
void main () { // Function
ADCON1 = 0x0F; // PORTA as digital IO
TRISA = 0xFF; // PORTA as i/p
TRISB = 0b ; // Lower 4 bits of Port B as output
PORTB = 0x00; // Initially off all LEDs
while(1) { // Endless loop
PORTB = ~PORTA; // read from PORTA & complement it // before send to PORTB }

40. To stimulate your thinking…
Take a look at the do-it-yourself question 2. You need to read a switch and then light up an LED based on the switch status.
Is it necessary to link the switch and the LED through wire connections?
Can we do the linkage through the software alone?
If your answer to (b) is “yes”, which hardware component is this flexibility due to ?