time delay in 16f876

A

amr_karimm

New Member
hi ,
i want to make a (asm) code for make 1 sec delay for pic 16f876 using (4mhz ) xt oscillator
any one can help me..
 
I have the same question. According to what other people adviced me, you use TMR0.
TMR0 with prescale 256. So we have 256*256 = 65536 Ms or 65.5 ms
if you loop it 15 times, so 65.5ms * 15 = 0.9825 sec
correct me If I am wrong.
Thanks
 
Try this if you not short of memory, use MPLAB stopwatch to test it.


Code: 
del		  EQU	0X74
delf1		EQU	0x75
delf2		EQU	0x76
main	call	DEL1sec
		 goto	main
DEL1sec	movlw	.6	;Delay start here,  
	movwf	del	;1.000001 sec
	movlw	.19        
	movwf	delf2       
	movlw	.174    ;fine tune with this number    
	movwf	delf1 	;173=999.99800 s
			;174=1.000001 s
			;175=1.000004 s
	decfsz	delf1 	;Start decrementing the file registers. 
	goto 	$-1
	decfsz	delf2 
	goto	$-3	
	decfsz	del
	goto	$-5
	return	;Go back if is done

STEVE
 
Hi, can you please tell me what else do I need to add for the code to make it work, I mean such things as specifying which PIC, including inc file... I am a nuewbie.
Thanks
 
patricktran said:
Hi, can you please tell me what else do I need to add for the code to make it work, I mean such things as specifying which PIC, including inc file... I am a nuewbie.
Thanks
Click to expand...

If you check my tutorials you will see everything you need, Tutorial 1 introduces timing delays and the reasons for them - an easy way to generate the code for a specific delay is to use the Delay Code Generator on the PICList at http://www.piclist.com.
 
Thanks for your advices.
I tried to get a delay of 1 sec by using busy loop. I think as follow:
1 sec = 1,000,000 instructions = 256 * 256 *15 = FF * FF * 0F
And I have the code:
Code: 
; Delay = 1 seconds
; Clock frequency = 4 MHz

; Actual delay = 1 seconds = 1000000 cycles
; Error = 0 %

	
d1   EQU    20h
d2   EQU    21h
d3   EQU    22h
	

			;999997 cycles
	movlw	0xFF
	movwf	d1
	movlw	0xFF
	movwf	d2
	movlw	0x0F
	movwf	d3
Delay1sec_0
	decfsz	d1, f
	goto	$+2
	decfsz	d2, f
	goto	$+2
	decfsz	d3, f
	goto	Delay1sec_0
	nop
   End
This code runs so long, it does not delay 1 sec. What is wrong with that?
Thanks
Pat
 
Oh, this code I got from the piclist code generator. It does with d1 = 0x08
d2=0x2F d3=0x03. I modified according to what I think: d1=0xFF, d2=0xFF d3=0x0F
 

As it reduce d1, it goto ... goto.... goto..., that is, it takes 2 + 2 + 2 cycles to do this loop. And it takes d1* ( 1 + 2 + 2+2) cycles to decrease d1 to zero. It's not only d1 cycles. So to d2. Therefore, you get a so long loop.

I've never used

d1 equ 20h.. so I don't remember, but if it's a const, how can you change it? I usually use variable in form that

d1 res 1
d2 res x
....

And as I need a preset value, I set in on Initialize fuctions. I do this because I made a standard form for all of my programs. As I more register, I add it to that block.
 
d1 equ 20 ; means d1 has an address of 20, which is a general purpose reg.
I think I can change it, cant I? Because it is just a general purpose reg, and therefore, it is a var, not const.
In a loop. I noticed:
1. goto <-> 2 instructions cycle
2. decfsz <-> 1 cycle if we dont skip, and 2 cycles if we skip....
Wow, this is so complicated. How come we calculate to get 1 sec delay by usign busy loop? Can someone give a sample code with explanation?
Thanks :?
 
Hi kemo
I'm also a student in the faculty of engineering. I need your help in microcontroller specially for smart card projects. I'm also from Egypt (Alex). I think we could be parteners in a very good workshops. We can alter experiences. I wish to have contact with you as soon as possible

Said
 
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