Pause

puts the controller into a "do-nothing" delay loop for 1 to 65535 units of 1000 instruction cycles (milliseconds at 4 MHz).

Precise time delays are an important part of most control program, since they allow the controller to synchronize with slower, real-world events.

Pause accepts a 16-bit number in hiB and lowB, and puts the controller into a do-nothing loop for that number of 1000-instruction-cycle units. With a 4-MHz clock (as in the BASIC Stamp) this amounts to time delays ranging from 1 to 65,535 milliseconds.

The routine requires a little processing time in addition to the internal delay loop, so the actual delay produced will always be 16 instruction cycles longer than specified. This amounts to an error of less than 2 percent for a 1-unit delay, and 0.24 parts per million for a 65,535-unit delay.

Demonstrating Pause.

To see Pause in operation, either run the program with the PSIM simulator, or connect the circuit below to an erasable PIC or PIC emulator, such as the Parallax downloader. Assemble and run PAUSE.SRC. When you apply power to the PIC, the LED will toggle once per second (assuming a 4 MHz clock). Try changing the value passed to Pause to adjust the flashing rate.

;
; ***************************************************************************
; ***  Bubble Software Parallax to PIC Source Converter. Copyright 1999.  ***
; ***  http://www.bubblesoftonline.com                 email: sales@picnpoke.com  ***
; ***************************************************************************
;
; PAUSE time
; A general-purpose delay routine that puts the PIC into a do-nothing
; loop for a 16-bit number of milliseconds (1 to 65535) at 4 MHz. Requires
; 16 cycles of overhead for call, return and other processing.

	P = pic16c55
	#include <16c55.inc>   ; processor assembler definitions
	_CONFIG _xt_osc & _wdt_off & _protect_off
 reset start

 org 8
hiB Res d'1' ; MSB of time.
lowB Res d'1' ; LSB of time.
temp Res d'1' ; temporary counter for Pause

; Device data and reset vector
 org 0

start        MOVLW d'0'                 ; Output through RB.
             TRIS 6h
             MOVLW d'3'                 ; Length of delay =
             MOVWF hiB
             MOVLW 0x00E8               ; 3E8h (1000 ms @ 4MHz).
             MOVWF lowB
             MOVLW d'255'               ; Toggle LED(s).
             XORWF 6h
             CALL Pause                 ; Wait 1 second.
             GOTO start                 ; Do it again.

; Upon entry, variables hiB and lowB hold the MSB and LSB of the
; number of milliseconds (1 to 65535) to delay.

Pause        COMF hiB                   ; Take twos complement
             COMF lowB                  ; of the 16-bit counter
             INCF lowB                  
             BTFSC status,z             ; If zero, lowB overflowed,
             INCF hiB                   ; so carry into hiB.
Pause_load   MOVLW d'248'               ; Set up for 1-ms loop.
             MOVWF temp
Pause_loop   NOP                        ; Do nothing.
             DECFSZ temp                ; Do more nothing.
             GOTO Pause_loop
             GOTO $+1                   ; 2-cycle "nop"
             INCF lowB                  ; lowB = lowB+1.
             BTFSC status,z             ; Overflow in lowB?
             INCFSZ hiB                 ; Yes: hiB=hiB+1, overflow?.
             GOTO Pause_load            ; No overflow: do it all again.
             RETLW 0h                   ; Overflow. Return to caller.
             
             
             end

; PAUSE time
; A general-purpose delay routine that puts the PIC into a do-nothing
; loop for a 16-bit number of milliseconds (1 to 65535) at 4 MHz. Requires
; 16 cycles of overhead for call, return and other processing.

	device	pic16c55,xt_osc,wdt_off,protect_off
	reset	start

	org	8
hiB	ds	1	; MSB of time.
lowB	ds	1	; LSB of time.
temp	ds	1	; temporary counter for Pause

; Device data and reset vector
	org	0

start	mov	!rb, #0 	; Output through RB.
	mov	hiB,#3		; Length of delay =
	mov	lowB,#0E8h	; 3E8h (1000 ms @ 4MHz).
	XOR	rb,#255 	; Toggle LED(s).
	call	Pause		; Wait 1 second.
	jmp	start		; Do it again.

; Upon entry, variables hiB and lowB hold the MSB and LSB of the
; number of milliseconds (1 to 65535) to delay.

Pause	NOT	hiB		; Take twos complement
	NOT	lowB		; of the 16-bit counter
	INC	lowB
	snz			; If zero, lowB overflowed,
	inc	hiB		; so carry into hiB.
:load	mov	temp,#248	; Set up for 1-ms loop.
:loop	nop			; Do nothing.
	djnz	temp,:loop	; Do more nothing.
	jmp	$ + 1		; 2-cycle "nop"
	inc	lowB		; lowB = lowB+1.
	snz			; Overflow in lowB?
	incsz	hiB		; Yes: hiB=hiB+1, overflow?.
	jmp	:load		; No overflow: do it all again.
	ret			; Overflow. Return to caller.

See also:

• http://www.piclist.com/techref/microchip/time.htm
• http://www.piclist.com/techref/microchip/delay/general.htm

Questions:

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