How to create a delay

[Lac]

In Nigle`s tutorial series, there is a example about delays:

Delay	movlw	d'250'			;delay 250 ms (4 MHz clock)
	movwf	count1
d1	movlw	0xC7
	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

I have been doing some math about this, and cant figure out how this can be 250ms.

Delay movlw d'250' ;1cycle
movwf count1 ;1cycle
d1 movlw 0xC7 ;1cycle
movwf counta ;1cycle
movlw 0x01 ;1cycle
movwf countb ;1cycle
Delay_0
decfsz counta, f ;1cycle
goto $+2 ;2cycles
decfsz countb, f ;1cycle
goto Delay_0 ;2cycles

decfsz count1 ,f ;1cycle
goto d1 ;2cycles
retlw 0x00 ;1cycle
[/code]

For the innerloop to run one time, it takes 1+2+2=5cycles, that would be 5*198=995 cycles for the first part of the inner loop, then we add the second little part. That would be 995+1+1+2+1+1=1001cycles for the whole first part.

The outer loops takes 1+2+1+1+1+1=7cycles to run 1 time, that would be 7*250=1750 cycles for the whole outer loop.

Total that would be 1750*1001+6=1751756cycles for the whole loop to run. And this is not 250ms. Could you please explain how this would be 250ms.

In advance, thanks.

 

[Nigel Goodwin]

That delay comes from the generator available on the PICList, it works fine :lol:

However, because of it's multiple interconnected loops it's VERY difficult to understand, I've never bothered trying!.

 

[kinjalgp]

Here is the one: **broken link removed**

 

[Nigel Goodwin]

Here is the one: **broken link removed**

It's not the same as the one on the PICList, but it gives similar results.