Hi Dwayne,
I wprked on a POCSAG pager way back in about 1979 or so . It was a
while ago ! so the memory is a bit hazy but:-
The decoder we used was actually a microcontroller (CMOS 6805) and
used a crystal  but there were hardware decoders used by the
competition and I'm pretty sure they didn't use crystals.

But they only had to decode - not encode and the encode spec is the
one that counts. I know we had to be able to obtain (and maintain) bit
sync over a range of bit rates, but can't remember what that range
was!

Is the POCSAG spec not available on the web? I seem to remember seeing
it somewhere.

Sorry I can't be more help

Richard Prosser

On 27 March 2010 07:03, Dwayne Reid <dwayner@planet.eon.net> wrote:
> Good day to all.
>
> I'm working on another project where I need to generate POCSAG
> data. =A0This is an add-on to an existing project.
>
> What I am wondering is if I need to have crystal accuracy for the baud ra=
te.
>
> The reason I ask is that the POCSAG specification has a very long
> preamble (minimum 576 alternating 1's & 0's), followed by up to 8
> frames of data, each with their own synchronization word. =A0The care
> that the writers of the spec have given to ensuring that the UART in
> the receiver can accurately synchronize to the incoming data rate
> makes me wonder if the pagers can tolerate a 0.5% or even a 1% error
> in data rate (baud rate).
>
> I can test against some real pagers but I'd rather hear it from
> someone who has expertise in the area. =A0The last thing I want to have
> happen is for it to work fine in my lab, then have it fail in the field.
>
> The reason I ask is that the existing project has a PIC with enough
> spare I/O and code space to stuff the POCSAG protocol into - but its
> using its internal RC oscillator. =A0The board layout is not conducive
> to hacking a crystal or resonator into.
>
> SO: if someone tells me that the POCSAG protocol is specifically
> designed to tolerate baud rate errors, I'll try it. =A0On the other
> hand, if I'm told that POCSAG will NOT tolerate baud rate errors,
> I'll plan to design up a little daughter board with its own PIC and
> crystal and such.
>
> Many thanks!
>
> dwayne
>
> --
> Dwayne Reid =A0 <dwayner@planet.eon.net>
> Trinity Electronics Systems Ltd =A0 =A0Edmonton, AB, CANADA
> (780) 489-3199 voice =A0 =A0 =A0 =A0 =A0(780) 487-6397 fax
> www.trinity-electronics.com
> Custom Electronics Design and Manufacturing
>
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