microcontroller technology oct 11 page 1 welcome to... seminar 5: i/o interfacing and programming...

Microcontroller Technology Oct 11

Welcome to . . .

Seminar 5:

I/O Interfacing and Programming

Reprinted with permission of the copyright owner, Microchip Technology Incorporated ©2000, 2001 and 2002. All rights reserved. No further reprints or reproductions may be made without Microchip Technology Inc.’s prior written consent.


Objectives:

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


PIN Diagram of PIC18F4520


PIC18F4520 I/O Ports

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!

I/O Ports: Facilitate the microcontroller in communicating with the outside world


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.


Registers

TRIS (Data Direction)

PORT (Read/Write DATA from or to I/O pin )

LAT (Data Latch register for read-modify-write)

Each port has 3 registers associated with it.

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


PORTx and TRISx

• There are five I/O ports in PIC18F4520. 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.


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.


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.


Using I/O Ports

1. Identify the Port to be used

2. If Port A, B and/or E is used, configure them as digital I/O pins by

Setting ADCON1

3. Configure the direction of each I/O pin Using TRISx (E.g Port A use TRISA)

4. Read from or Write to the pin or port Using PORTx


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’

ADCON1 = 0x0F; // Port A&E as digital I/O

TRISA = 0b11110000; //RA0-3 as o/p, RA4-5 as i/p

Solution:


Configure Port B pins 1, 2, 4, 6 and 7 as inputs and pins 0, 3 and 5 as output pins.

TRISB = 0b11010110 ;ADCON1 = 0x0f;

Example 2

Solution:


Example 3Given the circuit below, configure the directions of the I/O pins used.

Solution:

ADCON1 = 0x0F; // Port A&E as digital I/O

TRISA = 0b11000000; // Port A pin 0-5 are outputs

TRISC = 0b10110010; //RC0,2,3,6 as o/p, RC1,4,5,7 as i/p

RC1RC0

RC2RC3RC4RC5RC6RC7

RA1RA0

RA2RA3

RA5RA4


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.


PIC18F4520

Vcc

Vcc

J6

S3

S2

RB0/INT0

RA4

RB1

RB2

RB3

RD3

RD2

RD1

RD0

E

R/W

RS

Vcc

VEE

GND

GND1

RA3

RA2

RA1

DB7

DB6

DB5

DB4

DB3

DB2

DB1

DB0

LCD16 Char X 2 lines

Vcc

RX

TX

RC7

RC6

Vcc

Vcc

RA0

J9Piezo BuzzerRC2

Exercise 1


ADCON1 = 0x0F; // Port A, B &E as digital I/O

TRISA = 0b11110001; //RA1,2 & 3 as o/p, RA0 & 4 as i/p

TRISB = 0b11110000; // lower 4-bits as o/p

TRISC = 0b10111011; // RC2 & 6 as o/p, RC7 as i/p

TRISD = 0b11110000; // lower 4-bits as o/p

Solution

Exercise 1


Project Time!

Let us try to initialize the I/O ports for our Electronic Queueing System


Project: Queueing System

Hardware design

PIC18F4520

RB1

16x2 linesLCD Module

RC0RC1RC2RC3RC4RC5RC6RC7

D0D1D2D3D4D5D6D7

RE1RE2

E RS RW+5V

5V

RA1

RA0

RA2

+5.0V

RB0

Alarm

Q_request

Button 1

Button 2

Button 3


/* Initialise the IO ports */ADCON1 = 0x0F; /* PORTA, B & E as digital IO */

TRISA = 0xFF; /* PORTA as digital input ports – for buttons*/

TRISB = 0b11111110; /* RB0 as output pin for alarm */

TRISC = 0x00; /* PORTC as digital output data ports for LCD */

TRISE = 0b11111001; /* RE1 & RE2 as digital output pin for LCD control */


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;


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;


Example 4

Write a program segment to configure entire PORTC as output port and write 0x0F to PORTC.

TRISC = 0b00000000; // entire Port C as output

PORTC = 0x0F;

Solution


Example 5

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

LEDSolution

TRISD = 0b11111011; // RD2 as o/p

PORTD = 0x00; // or PORTDbits.RD2 = 0


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 = 0b10000001; // RD1 - 6 as o/p

PORTD = 0b01100010;


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 = 0b10000001; // RD1 - 6 as o/p

PORTD = ~PORTD;


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;


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;


Example 6

Write a program segment to configure the entire PORT C as input port and read in the value of PORT C.

TRISC = 0b11111111; // entire Port C as input

x = PORTC;

Solution


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

if (PORTCbits.RC3 == 0){

//continue the task if SW is closed}

Solution


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 BTurn ON or OFF the LED corresponding to switch being CLOSED or OPEN

PIC18F4520

RB3

LED R

+V

SW

RB2


Exercise 4

#include <p18f4520.h> //Directive

main(){/* initialize the I/O port */

ADCON1 = 0x0f; // Port B as digital

TRISB = 0b11111011; // 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

}

Solution


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.


#include <p18f4520.h> // Directive

#include<delays.h> // include library delay function

void main () { // Function

TRISB = 0b11110000; // 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

}

}

Exercise 5

Solution


Summary

You have just learnt:I/O ports of PIC18F4520Configuring of I/O pinReading from and Writing to I/O PinI/O Programming

We will learn more programming techniques next week on how to write a looping program.


Question 1:

Write a ‘C’ program segment to configure all the I/O ports for the circuit shown in next slide.

Do-it-yourself


PIC18F4520

RA4

RA3

RE2

RD7

RD6

RD5

RD4

RD3

RD2

RD1 g

a

f

be

c

d

d

c

e

b

f

a

g

5V

RC0RC1

+5V

M

RC2

RC3

RC4

TIME

+5V

SPEED

+5V

POWER ON

OFF

RB0RB1RB2RB3RB4RB5RB6RB7

16x2 linesLCD Module

E RS RW

D0D1D2D3D4D5D6D7

RE0

RE1

Speaker

Motor

HIGH

MID

LOW

+V


ADCON1 = 0x0F;

TRISA = 0bXX100111; //X can be 1 or 0

TRISB = 0x00;

TRISC = 0b11100000;

TRISD = 0b00000001;

TRISE = 0bXXX0X111;

Solution to Question 1:

/*TRISE bit4 must be written as 0 so that PORTD will be in General Purpose I/O mode */


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


Solution to Question 2:

#include <p18f4520.h> // Directive

void main () { // Function ADCON1 = 0x0F; // PORTA as digital IO

TRISA = 0xFF; // PORTA as i/pTRISB = 0b11110000; // 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 } }


To stimulate your thinking…

1. 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.

a) Is it necessary to link the switch and the LED through wire connections?

b) Can we do the linkage through the software alone?

c) If your answer to (b) is “yes”, which hardware component is this flexibility due to ?

microcontroller technology oct 11 page 1 welcome to... seminar 5: i/o interfacing and programming...

Documents

pins of ports

pic18f4520 io ports

direction of io port

adcon1 port

digital io pins

port register slide

b e io pins

g port