>
> Why? IIRC that is the second interrupt vector for an 18F
> series.

No, they are at 0x0008 (high priority) and 0x00018 (low priority).

So, there's no reason to be not using that code space.

> I suspect this is possibly a second reason for the
> led blinking intermittently, and interrupts are
> un-initialised, although they are not explicitly enabled, and
> so should not really worry the code.

Interupts are configured in a known state on POR, ie all disabled.

> The only possibility of
> trouble here is that the uncoded area may have something in
> it, but IIRC a memory word of 0xFFFF is a NOP for an 18F, but
> I could be wrong.

It is. 0x0000 and 0xFFFF are NOP, as is any unregognised program word.

However, if we assume that his programmer did not clear the program memory
(and why would it- if the programming phase had to erase first, it'd erase
the entire range of memeory which is 32k, and would take ages), then
remnants of whatever the OP originally posted probably remain here. And
considering he's been fiddling around trying to get this working, then it
seems fairly likely there are some branches, and set / clear / toggle portc
type instructions.

Jon

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