Delay function 4 seconds for pic 16f877A 20MHZ,, Assembly,,, help please!

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Hello everyone!

This is my first thread in the forum, I am really glad to have found it, its very helpful

I am just a beginner, and I want to find the correct function for the 16f877A to make a 4 seconds delay with 20MHZ

Thanks a lot
 

Hi and Welcome,

Use this very handy delay code generator, if you get stuck come on back.
Remember that 1 machine cycle ( the time for most instructions) is the Crystal Frequency /4


**broken link removed**

Code: 
; Delay = 4 seconds
; Clock frequency = 20 MHz

; Actual delay = 4 seconds = 20000000 cycles
; Error = 0 %

	cblock
	d1
	d2
	d3
	endc

Delay
			;19999992 cycles
	movlw	0xB5
	movwf	d1
	movlw	0x99
	movwf	d2
	movlw	0x2C
	movwf	d3
Delay_0
	decfsz	d1, f
	goto	$+2
	decfsz	d2, f
	goto	$+2
	decfsz	d3, f
	goto	Delay_0

			;4 cycles
	goto	$+1
	goto	$+1

			;4 cycles (including call)
	return
 

Thanks a lot

I tried this but I want the delay using the "nop" instruction and by having counters. Is this possible? Thanks a lot
 

Hi,

A delay using the NOP is just for one instruction, for your 4 seconds you need 20 million of them !
That is basically what that delay routine is doing, just that each loop takes several instructions, so it only needs counters d1,2 & 3

If you mean a delay using the Pics Timers ? - then see this first turorial, one of several good online ones.

**broken link removed**

Nigel's PIC Tutorial Page
 

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