languer
Joined: 09 Jan 2004
Posts: 144
Location: USA
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| Time travel |
 Posted: Fri Jul 30, 2004 2:38 pm |
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Years back, when I used PBP I worked on a few projects that needed variable delays. With the help from some persons on the PICLIST I was able to come up with this. Note that this was compiled from several sources (Andrew Warren, Dwayne Reid come to mind), I redefine it to suit my purposes and commented as much as possible.
| Code: |
(C)Copyright 2000 LR, compiled from various sources available on PICLIST (A Warren, D Reid, and others)
delayFn ; This function does the follwing (let delay=x) -> delay = 4*(delay/4)-1+8 = delay + 7cyc
movf _delay,W ; Save _delay in W for later use of 2 LSBs
BCF STATUS,0 ; Divide by four
RRF _delay ;
BCF STATUS,0 ;
RRF _delay ;
ANDLW 3 ; Extract 2 LSBs from original _delay - this number is the same amount of delay we need to
;before the 4x-1 loop
XORLW 3 ; 3 - W = W
ADDWF PCL ; Cycles to be added, by incrementing program counter:
NOP ; +3 cyc
NOP ; +2 cyc
timeLoop
NOP ; +1 cyc & 4 cycle delay loop begin
DECFSZ _delay ; +0 cyc
GOTO timeLoop
;+(_delay + 7)cyc -> total delay
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I also did a search on the PICLIST again, and came up with this:
| Code: |
From Dwayne Reid
;10 bit delay routine providing 1 cycle resolution. Works with both 12 & 14 bit core PICs.
;Original idea from Mike Harrison. This version by Dwayne Reid
;
;enters with upper 8 bits of delay in DELAYU, lower 2 bits in bits 1,0 of DELAYL
;bits 7..2 in DELAYL can be used as flags for whatever purpose desired.
;returns with W destroyed
Delay10bit ;delay is 10 bit value + 7 cycles ( + call + return, if any)
incf DELAYU,F ;correct for dec & test instead of test & dec
Dly10bLoop
comf DELAYL,W ;invert LSBs
decfsz DELAYU,F
goto Dly10bLoop ;coarse delay to closest 4 cycles
andlw b'00000011'
addwf PCL,F
nop
nop
nop
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