5.4 Microcontrollers II:

PIC16F84 Microcontroller

Dr. Tarek A. TutunjiMechatronics Engineering Department

Philadelphia University, Jordan

PIC Microcontroller

In the previous sequence, general microcontrollers and PIC architecture were introduced

In this presentation, PIC 16F84 will be used to elaborate microcontrollers. This will include• Pins description• Registers• Instruction set• Design & programming examples

PIC 16F84 Pins

General Specifications• Runs at 10 MHz• 8-bit data• 14-bit instruction• 1K Flash memory• One working register (W)

18 pins• VDD (+5V), VSS (gnd)• 13 I/O pins through two ports• Port A: 5-pins RA0 RA5

RA4 dual purpose (timer)

• Port B: 8-pins RB0RB7 RB0 dual purpose (Interrupt)

• !MCLR master clear (active low)• CLKIN (RC clock input)

PIC 16F84 Registers

All file registers are 8-bits

They are divided into: • SPR, specific purpose

• GPR, general purpose

The main specific registers are• PORTA: has 5 I/O bits

• TRISA: specifies the direction of port pins ‘1’ for Input & ‘0’ for Output

• PORTB: has 8 I/O bits

• TRISB: specifies the direction of port pins

• STATUS: bit 5 = 0 (1) page 0 (1)

• TMR0: 8-bit timer

• INTCON: Interrupt Control register

35 Instructions

Instructions used in next examples

MOVLW k move literal ‘k’ to W

MOVWF f move W contents to f

CLRF f clear f

INCF f increment f

BCF f,b clear bit ‘b’ in register ‘f’

BSF f,b set bit in f

BTFSS f,b bit test, skip if set

BTFSC f,b bit test, skip if clear

GOTO k go to address k

LED : circuit diagram

Writing to port (LED):

assembly program; This program is used to flash LED connected to pin RA1

STATUS equ 03h ; ‘equ’ is not an instructionTRISA equ 85h ; it is used by the assemblerPORTA equ 05h ; gives name to address value

bsf STATUS,5 ; Set bit 5 in Status register go to page 1movlw 00h ; Move ’00’ to W (working register)movwf TRISA ; Move contents of W to TRISA all outputbcf STATUS,5 ; Clear bit 5 in Status register go to page 0

Start movlw 02h ; Move ’02’ to Wmovwf PORTA ; Port A = ‘0000 0010’ RA1 ‘high’movlw 00h ; Move ’00; to Wmovwf PORTA ; Port A = ‘0000 0000’ RA1 ‘low’goto Start ; loop back to Start

Switches and LEDs:

circuit diagram

PIC16F84

+5V

Sw1clear

Sw2count

C

RA0

RA1

Vdd!MCLR

Vss

RB0

RB1

RB2

RB3

RB4

RB5

RB6

RB7

CLKIN

R

Reading & Writing; This program outputs binary count to LEDs connected at RB0 to RB7; Input switches connected to RA0 and Ra1 stops, starts, and resets the count

STATUS equ 03 ; assigns names to register addressesPORTA equ 05TRISA equ 85PORTB equ 06TRISB equ 86

bsf status, 5 ; go to page 1movwf 00 ; W = ‘0000 0000’movlw PORTB ; makes PORTB output (connected to LEDs)movwf ff ; W = ‘1111 1111’movlw PORTA ; makes PORTA input (connected to switches)bcf status,5 ; go back to page 0

Reset clrf portb ; PORTB = ‘0000 0000’ All LEDs off

Start btfss PORTA,0 ; Read RA0 (SW1), test RA0 value and skip if ‘1’goto Reset ; go back to Resetbtfsc PORTA,1 ; Read RA1 (SW2), test RA1 value and skip if ‘0’incf PORTB ; Increment PORTB PORTB = PORTB+1

goto Start

Summary

PIC 16F84 microcontroller runs at maximum frequency of 10 MHz

The input clock can either be RC circuit or oscillator

PIC 16F84 has 13 I/0 ports divided into 2 ports (A and B)

The main registers are: PORTA, PORTB, TRISA, TRISB, and STATUS

There are 35 instructions

Examples for simple I/O circuits (LEDs and Switches) were given