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PIC Microcontoller Delay Method

Delay X cycles (n-x) exclusive

from Nikolai Golovchenko

;-----------------------------------------------------------
;d0, d1, d2, ...dn      - counters
;d0 = 0..3              - least significant 2 bits
;d1,...dn = 0..255      - more significant 8, 16, 24, ... bits
;
;Total Delay =
;= d0+4*d1+4*256*d2+4*256*256*d3...+4*256^(n-1)*dn + overhead
;
;Overhead depends on a number of counters, see below

;First preincrement all counters except d0
;overhead = n cycles
        incf d1, f
        incf d2, f
        ...
        incf dn, f
;2 bit delay (d0 - 1 cycle resolution)
;overhead += 4 cycles
        comf d0, w
        andlw 0x03
        addwf PCL, f
Delay64Mx
Delay256Kx
        nop
Delay1Kx
        nop
Delay4x
        nop
;8 bit delay (d1 - 4 cycle resolution)
;overhead += 2 cycles
        decfsz d1, f
         goto Delay4x

;8 bit delay (d2 - 1024 cycle resolution)
;overhead += 3 cycles
        decf d1, f
        ;change d1 to 255, so previous loop
        ;(from Delay4x) will take
        ;255*4-1=1019 cycles
        ;we need to add 5 more cycles to get 1024.
        ;4 cycles are in this loop and
        ;another 1 cycle is a nop above

        decfsz d2, f
         goto Delay1Kx

;8 bit delay (d3 - 262144 cycle resolution)
;overhead += 3 cycles
        decf d2, f
        ;previous two loops (from Delay4x) will take
        ;1019+255*1024-1=262138 cycles
        ;we need to add 6 more cycles to get 262144.
        ;4 cycles are in this loop and
        ;another 2 cycles are above - two nops

        decfsz d3, f
         goto Delay256Kx

;8 bit delay (d4 - 262144*256 cycle resolution)
;overhead += 4 cycles
        decf d3, f
        ;previous two loops (from Delay4x) will take
        ;262138+255*262144-1 cycles
        ;we need to add 7 more cycles to get 4*256^3.
        ;5 cycles are in this loop and
        ;another 2 cycles are above - two nops
        nop
        decfsz d4, f
         goto Delay64Mx

;at this point we have a 34 bit one cycle resolution delay!
;Total Delay = overhead + 0..1.7e10 cycles
;overhead = 4+4+2+3+3+4 = 20 cycles
;-----------------------------------------------------------

And the same for a SX chip:

;-----------------------------------------------------------
;d0, d1, d2, ...dn      - counters
;d0 = 0..3              - least significant 2 bits
;d1,...dn = 0..255      - more significant 8, 16, 24, ... bits
;
;Total Delay =
;= d0+4*d1+4*256*d2+4*256*256*d3...+4*256^(n-1)*dn + overhead
;
;Overhead depends on a number of counters, see below

;First preincrement all counters except d0
;overhead = n cycles
        inc d1
        inc d2
        ...
        inc dn
;2 bit delay (d0 - 1 cycle resolution)
;overhead += 5 cycles
        mov w, /d0
        and #$03
        add PC, w
Delay256Kx
        nop
Delay64Mx
        nop
Delay1Kx
        nop
;8 bit delay (d1 - 4 cycle resolution)
;overhead += 2 cycles
Delay4x
        decsz d1
         jmp Delay4x

;8 bit delay (d2 - 1024 cycle resolution)
;overhead += 3 cycles
        dec d1
        ;change d1 to 255, so previous loop
        ;(from Delay4x) will take
        ;255*4-2=1018 cycles
        ;we need to add 6 more cycles to get 1024.
        ;5 cycles are in this loop and
        ;another 1 cycle is a nop above

        decsz d2
         jmp Delay1Kx

;8 bit delay (d3 - 262144 cycle resolution)
;overhead += 3 cycles
        dec d2
        ;previous two loops (from Delay4x) will take
        ;1018+255*1024-2=262136 cycles
        ;we need to add 8 more cycles to get 262144.
        ;5 cycles are in this loop and
        ;another 3 cycles are above - three nops

        decsz d3
         jmp Delay256Kx

;8 bit delay (d4 - 262144*256 cycle resolution)
;overhead += 6 cycles
        dec d3
        ;previous two loops (from Delay4x) will take
        ;262136+255*262144-2 cycles
        ;we need to add 10 more cycles to get 4*256^3.
        ;8 cycles are in this loop and
        ;another 2 cycles are above - two nops

        jmp $+1
        decsz d4
         jmp Delay64Mx

;at this point we have a 34 bit one cycle resolution delay!
;Total Delay = overhead + 0..1.7e10 cycles
;overhead = 4+5+2+3+3+6 = 23 cycles
;-----------------------------------------------------------

This is probably too small for SX :)

Code:

See also:


file: /Techref/microchip/delay/xb1crnm-ng.htm, 7KB, , updated: 2005/3/28 20:03, local time: 2018/2/24 19:53,
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