Data sheet states: "The FSR is a 5-bit wide register." (p. 18). However,
FSR<6:5> are bank select bits. On p. 13 is shown, that FSR<7> contains 1
after any kind of reset. Such way, the puzzle can be solved. I allow, it
is not very simple (I met also the same pitfall).

Imre

On Thu, 28 Jun 2001, Roman Black wrote:

> Thank you Andy and everyone else who helped! :o)
> I did my homework last night and tracked it down.
> My actual Vdd rise time is less than 70mS to
> reach 95% of Vdd. The datasheet spec is 0.05v/mS
> (100mS at 5v supply) so this is fine. I also hold
> all pins as outputs and set to low, which reduces
> the chance of startup latchup.
>
> After checking all my hardware I realised there
> was a software bug, caused by Microchip's shoddy
> documentation (Grrrrr!)
>
> With the 16c505 the FSR register bit7 CANNOT be
> cleared. Unlike other PICs. This is not mentioned
> in the datasheet anywhere, I found it with the
> simulator. Very nasty, the first thing I do on
> startup is clear all ram registers, using the
> typical FSR loop, and while I know FSR is only a
> 7 bit register (bit7 is unused), but whenever you
> read it to see where it is up to bit7 reads
> as 1.
>
> Very nasty, I don't mind software bugs when they
> are my fault, but that annoys me a lot...
> I have put big red notes on all the
> applicable pages in my 16c505 datasheet. :o(
> -Roman
>
>
>
>
>
>
> Andrew Warren wrote:
>
> > > I assumed that Microchip knew their stuff and when you set a PIC
> > > to internal RC osc and internal MCLR control this would be ok.
> > > After all, it's not hard to start up an RC osc is it?
> >
> > Roman:
> >
> > The failure of the RC oscillator is just a symptom of your REAL
> > problem, which is either that your Vdd rise time is too long or that
> > Vdd isn't starting its rise from < 0.7V.
> >
> > You only characterized your rise time as "less than" 150 ms. I don't
> > have a datasheet here, but I recall that Microchip's specified
> > Minimum Vdd Rise Rate is 0.05V/ms.
> >
> > Are you sure that your PIC's power supply is dropping to below 0.7V
> > before you switch it on?
>
> --
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>
>
>

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