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my 16f877a pic has a problem,it works well in c and i has a problen in assembly,help

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raju jaina

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this is my assembly prog to blink rd2,rd3 bits of 16f877a,after building and dumping it into mic..it does get started blinking,even i turned off the supply and on it again,i have to reset the mclr pin with ground then led blinks with voltage flucations......
but if i bump the prog written in c,all works well,i m also pasting my c prog below the assembly.i used nop for as i thought that my delay loop is getting stuct some where...so please try to help me...this problem is not with the single mic,i have two mic,they work the same.....
Code: 
processor	16f877A
	list		p=16f877A
	#include	"P16f877A.INC"
	__config	373ah

	cblock		20h
	count
	count1
	count2
	count3
	endc

                                 
		org	00h
	;	bcf		STATUS,RP1
	;	bsf		STATUS,RP0	
		banksel	ADCON1
		movlw	06h
		movwf	ADCON1
	;	banksel	TRISD

		movlw 	00H
		movwf 	TRISD
	;	movlw	1fh
	;	movwf	TRISD
	;	bcf		STATUS,RP0
	;	bcf		STATUS,RP1
		banksel	PORTD
back
	;	movlw	00h
	;	movwf	PORTB
		movlw	00h
		movwf	PORTD
	;	bsf		PORTD,RD3
	;	movwf	PORTD
		call 	delay
;		movlw	0ffh
;		movwf	PORTB
		movlw 	06h
		movwf	PORTD	
;	bcf		PORTD,RD2
	;	bcf		PORTD,RD3
	;	movwf	PORTD
	;	clrf	PORTB
	;	clrf	PORTD	
		call	delay
		goto	back


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nop
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nop
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		nop
		nop
		nop
		nop
		nop
		nop
	
;				movlw 	d'100'
;				movwf	count3
;d3				movlw	d'100'
;				movwf 	count2
;d2				movlw 	d'200'
;				movwf	count1
;d1				movlw 	d'200'
;				movwf	count
;d0				decfsz 	count
;				goto 	d0
;				decfsz	count1
;				goto    d1
;				decfsz	count2
;				goto 	d2
;				decfsz	count3
;				goto	d3
		return		

;---------------------------------------------------------------------------------------------------	

		end


cprog


 #include <pic.h>

__CONFIG(0x3F3A);


void main(void)
{
   unsigned int i;
	
   	TRISD = 0;
   /*   PORTB=1;
	TRISD = 0;
     PORTD=1;*/
    while(1)
     {
	RD2=1;
	RD3=1;
       for(i=0;i<15000;i++); 
      	RD2=0;
	RD3=0;	
       for(i=0;i<15000;i++);
	     
} 
}

Use CODE tags when posting your code.
Click to expand...
 
Last edited by a moderator:

Hi,

What a lot of NOPs !!:-D

You do not specify what oscillator you are using but the Config line specifies HS - thats 4 meg hz and above.

Have included a simple 500ms delay , based on a 4 meg hz crystal.

Code: 
      processor 16f877A
	list p=16f877A
	#include "P16f877A.INC"
	__config 373ah
	
	cblock 20h
	count
	count1
	count2
	count3#
	d1,d2,d3
	endc
	
	
	org 00h

	banksel ADCON1
	movlw 06h
	movwf ADCON1

	
	movlw 00H
	movwf TRISD

	banksel PORTD

back
	movlw 00h

	movwf PORTD

	call delay

	movlw 06h

	movwf	PORTD

	call delay

	goto back
	
	




delay250	movlw	d'250'				; delay 250 ms 
			movwf	d1
dly250_1	movlw	0xC7
			movwf	d2
			movlw	0x01
			movwf	d3
dly250_2
			decfsz	d2, f
			goto	dly250_3
			decfsz	d3, f
dly250_3	goto	dly250_2
			decfsz	d1	,f
			goto	dly250_1
			retlw	0x00



delay	call	delay250			; delay 500ms
		call	delay250
		return
   END
 

You haven't mentioned the oscillator frequency.

The thing is, the code works, but the blinking is too fast for you to notice. RD1 and RD2 are turning on and off but too fast for your eyes. You can check with an oscilloscope. Then you would see it.

However, all you need to do, is add a larger delay, one with counters and not NOPs, like the one posted by wp100.

You have around 1500 NOPs. With a 4MHz clock, that's 1500us (1.5ms). Too fast for you. With a 20MHz clock, that's 300us. You should replace that with a larger delay (in 100s of milliseconds or 1-2 seconds) and you would be able to observe the blinking properly.

Hope this helps.
Tahmid.
 

my crystal is 20 mhz,thanks for all the reply,i wll check it and see if it works....
 

The following Gooligum tutorials cover in depth the implementation of delay loops such as the delay routine presented by wp100:





Timer modules provide a more efficient method of producing delays without wasting cycles in delay loops:





Be sure and checkout the entire Gooligum Tutorial Collection:

**broken link removed**

BigDog
 

thanq u every one for ur help,the main problem is with hardware,before connecting led we put a limiting resistor right,i kept a 470 ohm,this used to draw a huge current so the mic used to get rese every time as its is getting overloaded,so now i kept a limiting resistor of 1k,it works good,so the all the problem is with hardware.thanq so much for u r help.....................................................
 

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