little help with my program please - simple count loop

**kud0s** · 7th July 2005 07:13 PM

hi there

here is what im trying to do:
a simple program that is acivated from a simple switch on an input pin on RA7 on the PIC, then the pic outputs a set number of pulses on anuther output pin in my case RA0. then when it has done this it outputs a simple finish pulse on RA1 pin.

Program:

here is my program to date, i have it working but im alittle lost on putting a simple count down or up loop into it so i can set it to putput for a set number of pulses as such.

any help would be grate

program is as follows

Code:

;indexer program - pules's to index with start and finish pules
	LIST	p=16F628A		;tell assembler what chip we are using
	include "P16F628A.inc"		;include the defaults for the chip
	__config 0x3F18			;sets the configuration settings (oscillator type etc.)

;defines
PULPORT	Equ	PORTA			;set constant PULPORT = 'PORTA'
TRIPORT	Equ	PORTA			;set constant TRIPORT = 'PORTA'
PORT	Equ	TRISA			;set constant for TRIS register
TRIG1	Equ	7
PULSE	Equ	0
FIN	Equ	1

;end defines

	cblock 	0x20 			;start of general purpose registers
		count1 			;used in delay routine
		counta 			;used in delay routine 
		countb 			;used in delay routine
		count2
	endc


	org	0x0000			;org sets the origin, 0x0000 for the 16F628,
					;this is where the program starts running	
	movlw	0x07
	movwf	CMCON			;turn comparators off (make it like a 16F84)

   	bsf 	STATUS,		RP0	;select bank 1
   	movlw 	b'10000000'		;set PortA 7 input rest outputs
   	movwf 	PORT			;set portA
	bcf	STATUS,		RP0	;select bank 0
	clrf	PULPORT			;set all outputs low

;main program

loop	btfss	TRIPORT, TRIG1
		call	TRIG			;call 
		goto	loop


;loops

TRIG	
;	movlw	d'10'			;pules output for steps
;lp	movwf	count2
	bsf	PULPORT, PULSE		;output 1 for pulse RA0
	call 	delay			;call delay
	bcf	PULPORT, PULSE		;turn off RA0
	call	delay
;	decfsz	count2,	f
;	goto	lp
	bsf	PULPORT, FIN		;turn on RA1 for finish pulse
	call	delay			;call delay
	bcf	PULPORT, FIN		;turn off RA1 for Finihs
	retlw	0x00

delay	movlw	d'150'			;delay 250 ms (4 MHz clock)
	movwf	count1
d1	movlw	0xC7			;delay 1mS
	movwf	counta
	movlw	0x01
	movwf	countb
Delay_0
	decfsz	counta, f
	goto	$+2
	decfsz	countb, f
	goto	Delay_0

	decfsz	count1,	f
	goto	d1
	retlw	0x00

	end

once again thanks 8)

**kud0s** · 7th July 2005 07:30 PM

forgot to say

the lines in the TRIG loops that i commented out with ; was wht i had a play with to do a loop for a set ammoutn which did not work, it seems to get stuck in that loop!!

lines
; movlw d'10' ;pules output for steps
;lp movwf count2

and
; decfsz count2, f
; goto lp

does any one know why?

**williB** · 7th July 2005 07:50 PM

countdown loop complements of Mike ..

Code:

        movlw   d'33'           ; use 33 (20 mhz) or 13 (8 mhz)   |B0 
        movwf   TEMP            ;                                 |B0 
ACQ     decfsz  TEMP,F          ; wait 20 usec  to acquire        |B0
        goto    ACQ

**Nigel Goodwin** · 7th July 2005 08:40 PM

Originally Posted by kud0s

forgot to say

the lines in the TRIG loops that i commented out with ; was wht i had a play with to do a loop for a set ammoutn which did not work, it seems to get stuck in that loop!!

lines
; movlw d'10' ;pules output for steps
;lp movwf count2

and
; decfsz count2, f
; goto lp

does any one know why?

As williB's example shows, you are jumping back one line too far, so 'count2' continually gets reloaded, and can never reduce to zero to end the loop.

**kud0s** · 7th July 2005 08:59 PM

thanks guys

top stuff fully sorted it now time to refine it up

**mstechca** · 7th July 2005 09:40 PM

Originally Posted by kud0s

hi there

here is what im trying to do:
a simple program that is acivated from a simple switch on an input pin on RA7 on the PIC, then the pic outputs a set number of pulses on anuther output pin in my case RA0. then when it has done this it outputs a simple finish pulse on RA1 pin...

Dont even bother using a microcontroller.

Use a 4060 binary counter. Your button will activate the reset function on the chip, and connect the device that receives the pulses to Q0 since every odd number in binary has a 1 at the end of it. Now you will get pulses. Once the desired bit pattern is received, force the clock to stop.

Here is an example:

If you want the chip to pulse 4 times, connect the chip as follows:
connect Q0 to output
connect Q3 to the input of a NOR or an OR gate.
connect your clock to the other input of the same gate.
The output of the gate is connected to the clock pin on the counter.

As soon as the chip is initialized, Q0 will be pulsed 4 times and that's it.
When the reset pin is activated, the process starts over.

Here's how the counter does it:

at initialization:

....0000
....0001
....0010
....0011
....0100
....0101
....0110
....0111
....1000
....1000
....1000

Notice how the right most column switches between 1 and 0? this is the best place to take the pulse at normal clock speed. For a pulse half the clock speed, connect the output to Q1 instead. At the end, the binary result 1000 remains true until the reset is activated. Why? because a "1" is applied to the gate and the output of the gate is fixed when a "1" is applied to at least one input. If bit 4 or Q3 wasn't activated, then the output is determined by the clock, and depending on the gate, it could be inversed.

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