How to check whether it is ZERO or not? - Electronic Circuits Projects Diagrams Free

Suraj143 · 20th September 2007, 04:46 AM

Hi I have a COUNT variable. When power up the PIC don’t know what value in it. (It depends on the last saved value in EEPROM)

I want to check whether it is ZERO or other. If it is zero I want to goto NORMAL program. If not zero I want to goto UPDATE routine.

Here is my code please tell me am I right?

Code:

	movf	COUNT,W		;get the count value
	xorlw	00h		;compare with zero
	btfss	STATUS,Z	;check the ZERO bit
	goto	UPDATE		;NO, it is not ZERO
	goto	NORMAL		;YES, it is ZERO

blueroomelectronics · 20th September 2007, 04:55 AM

Yep that'll work. MPASM also has a couple of macros built in to make that eaiser.

so..

Code:

  movf   COUNT,W   ;sets the z flag
  bz     NORMAL    ;it's zero so branch
  goto   UPDATE    ;not zero so goto UPDATE

PS movf will set the zero flag, you don't need the xor.

Pommie · 20th September 2007, 05:10 AM

Another useful way to test for zero is movf COUNT,F. This will set/clear the zero flag without corrupting W.

Mike.

Suraj143 · 20th September 2007, 05:23 AM

Oh I see now I got it.Everywhere I'm corrupting W I must prevent this by moving the value to the FILE register.

Also built in macros really helpful.I must give a try for that.

Thank you both of you for the instant replies.

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20th September 2007, 04:46 AM	(permalink)
Suraj143	How to check whether it is ZERO or not? Hi I have a COUNT variable. When power up the PIC don’t know what value in it. (It depends on the last saved value in EEPROM) I want to check whether it is ZERO or other. If it is zero I want to goto NORMAL program. If not zero I want to goto UPDATE routine. Here is my code please tell me am I right? Code: movf COUNT,W ;get the count value xorlw 00h ;compare with zero btfss STATUS,Z ;check the ZERO bit goto UPDATE ;NO, it is not ZERO goto NORMAL ;YES, it is ZERO

20th September 2007, 04:55 AM	(permalink)
blueroomelectronics	Yep that'll work. MPASM also has a couple of macros built in to make that eaiser. so.. Code: movf COUNT,W ;sets the z flag bz NORMAL ;it's zero so branch goto UPDATE ;not zero so goto UPDATE PS movf will set the zero flag, you don't need the xor. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

20th September 2007, 05:10 AM	(permalink)
Pommie	Another useful way to test for zero is movf COUNT,F. This will set/clear the zero flag without corrupting W. Mike.

20th September 2007, 05:23 AM	(permalink)
Suraj143	Oh I see now I got it.Everywhere I'm corrupting W I must prevent this by moving the value to the FILE register. Also built in macros really helpful.I must give a try for that. Thank you both of you for the instant replies.