On May 16, 2007, at 11:54 AM, Lee Marshall wrote:

> wouldnt clearing pclath modify the program counter and
> before i could move to to address 0.
>
This seems to be a common misunderstanding.  PClatH is NOT part
of the program counter.  Changing PClatH does not have any
effect upon the PC, and changing the PC (ie Call, Goto, Ret)
does not change PClatH.

The "lat" part of PClatH stands for "LATCH"; this register (or
these bits in some other register) latch the bits that will be
moved into PCH (the ACTUAL PC register, high bits) the next time
an instruction modifies the PC (but doing something to PCL directly.)
So "goto" takes 8 low bits from the instruction itself, and the
remaining bits from the latch, while "ret" restores all (>8) bits
of the PC but doesn't do anything to PClatH.

BillW
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