PIC18 Branch, simple question.

On 3 May 2005 03:54:01 -0700, "Lanarcam" <lanarcam1@yahoo.fr> wrote:

>> Although "branch" instructions usually take as a parameter, the
>> *distance* to the target, every assembler that I have ever seen
>> takes *the address of the target itself*, and assembles that into
>> the "distance to jump".
>
>For the good old M68K you have BRA dest or JMP dest. In both cases
>dest is the address of the destination, but the machine code for
>BRA has a pc relative displacement whereas for jump it has an
>absolute address.

The interesting question is relative to _which_ PC value ? For various
architectures there might be at lest the following cases:

1. The value of the PC instruction (I can't remember any)
2. The PC value between OPcode and displacement (especially with 8 bit
processors)
3. The PC value of the _next_ instruction (most common)

>Ever used BRA * ?

Are you trying to destroy that memory location by overheating the
core? :-)

Paul

Paul Keinanen wrote:
> On 3 May 2005 03:54:01 -0700, "Lanarcam" <lanarcam1@yahoo.fr> wrote:
>
> >> Although "branch" instructions usually take as a parameter, the
> >> *distance* to the target, every assembler that I have ever seen
> >> takes *the address of the target itself*, and assembles that into
> >> the "distance to jump".
> >
> >For the good old M68K you have BRA dest or JMP dest. In both cases
> >dest is the address of the destination, but the machine code for
> >BRA has a pc relative displacement whereas for jump it has an
> >absolute address.
>
> The interesting question is relative to _which_ PC value ? For
various
> architectures there might be at lest the following cases:
>
> 1. The value of the PC instruction (I can't remember any)
> 2. The PC value between OPcode and displacement (especially with 8
bit
> processors)
> 3. The PC value of the _next_ instruction (most common)
>
> >Ever used BRA * ?
>
> Are you trying to destroy that memory location by overheating the
> core? :-)

That's how, in the case of a serious error, the device was reset
thanks to a watch dog who wasn't fed;)