John Nall wrote:
> someone like Olin might jump in and tell
> me how to do it with just one instruction. :-)
>
> Anyway, in the meantime, I have discovered a few more like that.   So be
> it.  Not very elegant, though.

There are a few operations for which a PIC 18 has a specific instruction
that the PIC 30 does not.  There are a few skip instructions, but there are
far more BRA instructions for conditionals.  Once you go native on the 30F
you won't use the file register operations much, and generally do arithmetic
decisions with BRA instructions.

The one I notice missing most is some sort of decrement and test in one
instruction, like DECFSZ on other PICs.  The PIC 30 does have the DO
instruction for looping, but it only has two hardware levels so you reserve
that for the rare bit of truly critical code.

You generally don't use file register instructions because these can only
reach a subset of the address space.  You can define some critical words to
be in near memory so that these instructions can be used, but you don't want
to do that generally in non-critical code (even though the RAM space of most
dsPICs is small enough so that all of it is "near", it's just not a good
practise.).

I hadn't jumped in here before because I personally don't see much point in
a PIC 18 to PIC 30 translator, other than it's something you want to do just
because you want to do it.  The differences in peripherals are going to make
all put purely "internal" code pretty much impossible.  You can make a PIC
30 stand on its head and waste a bunch of cycles and sortof act like a PIC
18 some ot the time with a lot of work.  I'd rather spend the time to recode
the application into native PIC 30 and get the full benefit of the
processor.  If you aren't pushing the speed, then why isn't the 18F good
enough in the first place?


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