PIC 100KHz Square Wave generator
Following on from the LED flasher circuit, we
can reduce the delay in the loop to 10uS (10 microseconds) and produce
a 100Khz square wave.
Given a 4 Mhz PIC 16C84, the program below will generate a 100Khz
square wave on PORTA bit 0 (i.e. pin 17). This little program is
useful for testing oscilloscopes (though it is not very accurate).
This program is available as:
; Mark Crosbie 9/12/98
; Scope test program. Generate a 100Khz square wave.
;
; The Program simply sets up Bit 0 of Port "A" to Output and then
; loops, setting the value alternatively low and high
;
; Hardware Notes:
; Reset is tied through a 4.7K Resistor to Vcc and PWRT is Enabled
; A 220 Ohm Resistor and LED is attached to PORTA.0 and Vcc
;
; device pic16c84
include "p16c84.h"
__CONFIG _CP_OFF & _WDT_OFF & _XT_OSC & _PWRTE_ON
; Mainline of FlashFast
org 0
clrf PORTA ; Clear all the Bits in Port "a"
clrf STATUS
bsf STATUS, RP0 ; Goto Bank 1 to set Port Direction
bcf TRISA, 0 ; Set RA0 to Output
bcf STATUS, RP0 ; Go back to Bank 0
Loop
movlw 1 ; Turn on the LED on Port A
movwf PORTA ;
movlw 5
call mdelay ; 5 uS delay
movlw 0 ; Turn off the LED on Port A
movwf PORTA ;
movlw 5
call mdelay ; 5uS delay
goto Loop
; counter variables
CNT dt 0
CNT1 dt 0
CNT2 dt 0
CNT3 dt 0
CNT4 dt 0
; delay for w uS. Set the w register to the desired delay value
MDELAY:
MOVWF CNT ;LOAD DELAY TIME
COUNT: NOP ;TWO NO OPERATIONS
NOP ;TO OBTAIN THE DELAY
DECFSZ CNT,1 ;DECREMENT THE COUNTER
GOTO COUNT ;GOTO COUNT IF NOT FINNISHED
RETURN
end
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