Hi Mike,

> The examples below show the difference:
>         xorwf   reg     ; reg = reg xor W, assembler issues
> warning.
>         xorwf   reg,f   ; reg = reg xor W
>         xorwf   reg,w   ; W = reg xor W
>
> The xorwf in the example can be any of the following:
> addwf, subwf, iorwf, xorwf, andwf : use W as part of the operation.
> movf, incf, decf, swapf, rlf, rrf, comf : Ignore W on input.
> incfsz, decfsz : Ignore W on input, skip if result is 0.
> clrf : a special case as the assembler always forces ,f but won't allow
> it explicitly.  The "instruction" clrw is internally clrf xxx,w.

This last bit you wrote.

  clrf xxx,w

Does one suppose that it will do a read on a port if the
xxx were to be one of the valid port registers.  Just thinking
about the implications when (foolhardily) using interrupt on
change on portB while running.  Will a badly assemble formated
clrw instruction cause the port registers to be updated without
having any apparent effect on the register.  Is this one way
to check if you are running on silicon or a simulator :-)

Cheers
--
Kalle Pihlajasaari   kalle@ip.co.za   http://www.ip.co.za/ip
Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle

DonTronics, Silicon Studio and Wirz Electronics uP Product Dealer