PIC: 16F How to toggle a single bit in file register

[eblc1388]

Hi guys,

On a 16F877, I have set up eight flags using a single register called "flags" and I need to change them or toggle them individually.

I know I can test the bit and change it, but is there an easy way to just toggle a single bit, for example?

 

[Nigel Goodwin]

Hi guys,

On a 16F877, I have set up eight flags using a single register called "flags" and I need to change them or toggle them individually.

I know I can test the bit and change it, but is there an easy way to just toggle a single bit, for example?

It's VERY, VERY simple - you should read the datasheet, there's only 35 instructions!.

But see BSF (to set a bit), and BCF (to clear a bit).

 

[eblc1388]

Thanks Nigel, but I like to "toggle" the bit not set or clear it.

Nevermind, I figured it out myself.

movlw    B'00001000' ;toggle bit3
xorwf    flags,F

 

[Jay.slovak]

on PIC18F, you would just use BTG (Bit togle) instruction

 

[Joel Rainville]

Thanks Nigel, but I like to "toggle" the bit not set or clear it.

Nevermind, I figured it out myself.

movlw    B'00001000' ;toggle bit3
xorwf    flags,F

Exactly 8)

And a little optimization trick : say you frequently toggle 2 or multiple flags at the same time, you can OR them together as assembler #defines and use the #defined value to toggle both flags in 1 instruction

#define		FLAG1		B'00000001'
#define		FLAG2		B'00000010'
#define		FLAGS1n2   FLAG1 | FLAG2

[...]

	movlw	FLAGS1n2
	xorwf	[file]

Very useful for some algorithms... Sorry if I'm being Captain Obvious here :lol:

 

[Joel Rainville]

on PIC18F, you would just use BTG (Bit togle) instruction

Yes, but as you can see from my previous example, xorwf is more "powerful". If I am not mistaken, BTG limits you to 1 bit at a time?...

 

[Jay.slovak]

on PIC18F, you would just use BTG (Bit togle) instruction

Yes, but as you can see from my previous example, xorwf is more "powerful". If I am not mistaken, BTG limits you to 1 bit at a time?...

Actually yes, good point here (I didn't think about that).