You can not swap the W-reg in tha
(the first) way. The second example
is OK.
W-reg is not accessable as an SFR.
And of course it's in the manuals... :-)

Note, do *not* use "0" and "1" as the
destination bit in commands, use "W" and "F"
instead. Much clearer. That is :

 > MOVLW 0x4F
 > MOVWF TEMPREG
 > SWAPF  TEMPREG, W

Than it also clear why :

 > MOVLW 0x4F
 > SWAPF W, W

didn't work, right ?
SFR with adress "0" is *not* the W-reg...

Jan-Erik.



Anand Gadiyar skrev:
> Hi all,
> 
>    I've been playing around with a PIC 16F877A now. I'm a newbie. I
> seem to have found strange behavior while using the SWAPF instruction.
> 
> Here's the code I tried in MPLAB SIM.
> 
> MOVLW 0x4F
> SWAPF W,0
> 
> This code seems to be zeroing out the W register instead of exchanging
> the nibbles like it's meant to. I had to work around it by writing the
> word to a temporary register and swapping it like this:
> 
> MOVLW 0x4F
> MOVWF TEMPREG
> SWAPF  TEMPREG,0
> 
> This gives me 0xF4 in W register.
> 
>    I couldn't find this in the manuals. Any comments? Is the PIC
> supposed to behave this way? Then, why isn't it there in the
> Instruction Reference.
> 
>    Please forgive me if I'm missing something. Like I said before, I'm a newbie.
> 
> Thanks in advance,
> Anand
> 
> _______________________
> Anand Gadiyar,
> CEDT,
> Indian Institute of Science,
> Bangalore - 560 012
> India
> _______________________

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