Toggle command

[mr.sneezy]

I recently (ok, today) discovered that the PBP TOGGLE command can toggle a variable, as well as output pins (which I used regularly).

I just tried a bit var, yep works. Goes 0-1-0-1.

Mode var bit
Mode_Butn var PortB.1

If mode_Butn = 0 then
        Toggle Mode
        LCDout $FE,$C8,"Mode",DEC1 mode
        Pause 500
    Endif

OK, the PBP manuals description is:
TOGGLE Pin

Invert the state of the specified Pin. Pin is automatically made an output. Pin may be a constant, 0 - 15, or a variable that contains a number 0 - 15 (e.g. B0) or a pin name (e.g. PORTA.0).

So what does the 'variable that contains a number 0-15 (e.g. B0)' mean ?

Does that mean that you can toggle any bit in a word, or just a number up to #15, or 0-15 variables ?

[Darrel Taylor]

TOGGLE should ONLY be used on PIN's!

Yes, it does toggle the bit of any Register.Bit combination that you pass to it.
What's not so obvious is that it also attempts to set the TRIS register associated with that PIN.

On a 16F, it adds 80h to the specified PORT's register.
On an 18F, it adds 12h, and in both cases it clears the matching bit to insure the PIN is set to output.
It doesn't care if it's not really a TRIS register. It clears it anyway.

If you aren't actually toggling a PIN, the results can be RANDOM because it's overwriting BIT's in other variables.

A better method of toggling a BIT in any register is to use the Bitwise NOT operator (~) or the Logical NOT (! or NOT).

So what does the 'variable that contains a number 0-15 (e.g. B0)' mean ?

The PIN numbers are a Basic Stamp compatibility issue.
On some PIC's 0 = PORTB.0, on other PIC's it's PORTA.0, on 12F's It's GPIO.0.
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[mr.sneezy]

Hi again Darrel,

I think we crossed wires somewhere. I'm not toggling a port register, I toggled one bit inside a ram register, assigned by PBP (Mode var Bit). The 0-1-0-1 was the bit variable result displayed via the LCD routine, nothing to do with a port at all other than I use a pin to make the bit value toggle once...

Does that change your response to toggling a RAM variable ?

Anyway. If you don't use Toggle to swap a ram 'bit variable' value from 0 to 1 and vice versa, how would you do it in minimal code ?
Martin

[Darrel Taylor]

I think we crossed wires somewhere. I'm not toggling a port register, I toggled one bit inside a ram register, assigned by PBP (Mode var Bit) ...

Does that change your response to toggling a RAM variable ?

There's probably some wires crossed, but I'd place a large bet that it's not on this end.

That's exactly what I'm talking about.

If you use TOGGLE on any BIT other than a PIN, you will be inadvertently clearing a BIT in another RAM location. The results will be unpredictable.

[mr.sneezy]

I see. Yes, crossed at my end (as always). Interesting. In my application it's working well and seems to be stable thus far... Lucky I guess.

I should change it. So you use this, if Mode is a bit var ?

Mode = Mode ^ %00000001 ' Reverse state of bit var Mode

[Darrel Taylor]

Luck always runs out eventually. The more variables you have in the program ... the more likely to see the problem.

Mode = Mode ^ %00000001 ' Reverse state of bit var Mode

That's valid!

So is ...

Mode.0 = !Mode.0
Mode.0 = NOT Mode.0
Mode.0 = Mode.0 ^ 1
Mode.0[0] = ~Mode.0[0]
...

Anything but TOGGLE, unless it's a PIN.
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