Thank for all the answers, I think I stick to resonator and RS485, I think I
am going to implement 1 master multiple slave on a half duplex mode, I think
that shouldn't be a bigger headache than unreliable comms.

On 2/26/02 8:28 PM, "Olin Lathrop" <olin_piclist@EMBEDINC.COM> wrote:

>> 1) If I use intrc can I still use the UART ???
>
> This is strictly a matter of timing tolerance between the two devices on the
> line.  The receiver looks for the leading edge of the start bit, then times
> the other bits relative to that.  At 8 data bits, the center of the last bit
> is 8 1/2 bits from the leading edge of the start bit.  The absolute maximum
> tolerable error is therefore 5.88%, which causes the last data bit to be
> sampled at its edge instead of the middle.  Most receivers sync everything
> to a 16x baud clock, so there is an additional small uncertainty in
> measuring the leading edge of the stop bit.  Of course, you don't want to be
> near the guaranteed to fail limit anyway.  I like to see no more than about
> 1/4 bit time error by the last bit, or about 3% clock mismatch betwen
> receiver and transmitter.
>
> Keep in mind that this is the combined error between receiver and
> transmitter.  If you know the other end is right on (like a PC, for
> example), then you can get away with 3% mismatch in the PIC.  If you've got
> two PICs with uncertain oscillators, then they each need to be within 1.5%.
>
>
> ********************************************************************
> Olin Lathrop, embedded systems consultant in Littleton Massachusetts
> (978) 742-9014, olin@embedinc.com, http://www.embedinc.com
>
> --
> http://www.piclist.com hint: PICList Posts must start with ONE topic:
> [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads
>
>

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads