Question

Use assembly instruction decfsz and other associate instructions to create delays for the generation of a 500Hz tone continuously via port C pin 5. Set up the related registers accordingly. Set internal clock to 4MHz (15 points)

Answer 1

Answer:- The 500 Hz has time period equal to 2 ms. Thus high time is of 1 ms and low time is of 1 ms. The count for 1 ms delay is-

n = 0.001 * 4000000/4 = 1000

The PIC18F assembly code is written below-

Count1 EQU 0x70 ;at address 0x70 Count1 variable is defined
Count2 EQU 0x71 ;at address 0x71 Count2 variable is defined

BCF TRISC, 5 ;make port C pin 5 as output

Loop:
BSF PORTC, 5 ;set port C bit 5
CALL Delay ;call the delay subroutine
BCF PORTC, 5 ;clear the bit 5
CALL Delay ;call the delay subroutine
GOTO Loop ;Loop the same thing infinitely

Delay:
MOVLW 0x05 ;W = 5
MOVWF Count2 ;Count2 = 5
Repeat:
MOVLW 0xC8 ;W = 200
MOVWF Count1 ;Count1 = 200
Here:
DECFSZ Count1 ;decrement the value of Count1 and skip next line if Count1 is zero
GOTO Here ;go to label Here
DECFSZ Count2 ;decrement the value of Count2 and skip next line if Count2 is zero
GOTO Repeat ;go to label Repeat
RETURN ;return to next of the subroutine call