On 2010-11-28 23:59, David Duffy (AVD) wrote:
> Olin Lathrop wrote:
>> David Duffy (AVD) wrote:
>>
>>> I am using INDF0 for reading the receive buffer.  It is the same code
>>> I've used countless times before.
>>>
>>
>> Are you doing this in the interrupt routine and forgot to save/restore t=
he
>> FSR?
>
> I am using INDF0 in the serial receive ISR, as well as in tasks
> triggered by flags in the main loop.
>
> I'm not saving / restoring them in the ISR, as I understand this
> particular chip does that by itself.
> David...
>

They are. But of course you have to re-init them at each
entry to the ISR, they are not preserved between two interrupts.
You didn't say you don't, but just to clearify.

B.t.w, this is what the PIC16F193X/LF193X datasheet says :

Upon entering an interrupt, the return PC address is
saved on the stack. Additionally, the following registers
are automatically saved in the shadow registers:
=95 W register
=95 STATUS register (except for TO and PD)
=95 BSR register
=95 FSR registers
=95 PCLATH register
Upon exit from the Interrupt Service Routine, these registers
are automatically restored. Any modifications to
these registers during the ISR will be lost. Depending
on the user=92s application, other registers may also need
to be saved.


What I do not understand is why you don't read the receive
buffer (RCREG) directly. Why go through the index registers ?
The reading will always be from the same fixed address (RCREG)
so I do not see the need for any "indexing" here !?


--=20
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