Jamie Lawson (jlawson@evbhort.uoguelph.ca) wrote:

>My question has to do with accessing registers in different pages,
>for example;
>
>To access PORTA you must set the page bits to point to
>page 0 and refer to this register as loaction 0x05.
>To access TRISA you must set the page bits to point to
>page 1 and refer to this register as location 0x85.
>
>Just out of curiosity, why is it necessary to change pages AND refer
>to a different location? Why do you not simply change page registers
>and reference the same relative register. In the above example TRISA
>would be on page 1 but be register 0x05?

Jamie:

It's not necessary to do both.  In fact, if you look at the opcode
generated by a "MOVWF 0x85", you'll see that it's identical to the
opcode for "MOVWF 0x05"... That's why the page-select bits are required
in the first place.

The Microchip assembler will even give you a warning when it assembles
your source code, telling you that it's truncating the register address.

-Andy


--
Andrew Warren - fastfwd@ix.netcom.com
Fast Forward Engineering, Vista, California