Cirrus Logic AN88 - Manual (Page 12)

AN88
12 AN88Rev2
;*************************************************************************************
;* Routine - delay
;* Input
- Count in register A
;* Output - none
;* This subroutine delays by using count from register W. The PIC16F84
;* development board uses a 10 MHz clock (E = 2.5 MHz), thus each cycle is
;* 400 nS. This delay is approximately equivalent to
;* (400ns)*(1545)*(count value), (a count of 720 provides a 445ms delay).
;*************************************************************************************
delay
MOVWFCOUNT ; Put the delay count into COUNT
outlp CLRF TEMP ; TEMP used as inner loop count
innlp NOP ; 1 cycle
NOP ; 1 cycle
NOP ; 1 cycle
NOP ; 1 cycle
DECFSZ TEMP,1 ; FF-FE, FE-FD, ....1-0 256 loops
; 10 cycles*256*500ns=1.28 ms
goto innlp ; If count not done repeat loop
DECFSZ COUNT,1 ; Countdown the accumulator
goto outlp ; 2569 cycles*500ns*A
RETURN ; Exit subroutine
;*************************************************************************************
;* Interrupt Vectors
;*************************************************************************************
NOT_USED RETFIE
ORG 0x04 ; Originate Interrupt Vector here
goto NOT_USED ; No Interrupts Enabled
end ; End Program Listing