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PICList Thread
'xtals, daisy-chain'
1995\07\13@180640 by Kalle Pihlajasaari

Says Martin Kirk
> > I have designed in a system with 6 PICs using one crystal but have
> > not tried it yet, I expect that it will work though.
>         I too have used two PICs with a 20MHz crystal.  I have  upgraded my
> design to four PICs but I am not as bold as Kalle.  I spoke to Microchip
> about this very subject.  They told me that they have had successful
> results with up to three PICs at 20 MHz.  They would not make any
> guarantees for four because of the limited drive capability of the OSC2
> output.  It is designed to drive a crystal, not multiple outputs.  Also
> it seems I remember that they cautioned that I might
> need to adjust the capacitors used with the crystal because of the extra
> capacitance of the loads (help me out here Microchip...are you listening?).
> Someone (not at Microchip) suggested a buffer to drive the extra PICs.
> Of course the downstream PICs would run behind by the delay period of
> your buffer.

I plan to daisy-chain the osc-out pin of the xtal driven PIC to the
osc-in of the second one and the osc-out of PIC-2 to osc-in of PIC-3
and so on.  Clock phase is unimportant to me as the PIC's are doing
independant tasks.
Kalle Pihlajasaari
Interface Products     Box 15775, Doornfontein, 2028, South Africa
+27 (11) 402-7750      Fax: +27 (11) 402-7751

1995\07\13@190404 by mlk

picon face
On Thu, 13 Jul 1995, Kalle Pihlajasaari wrote:

{Quote hidden}

       I may be mistaken but I believe that in order to use an external
clock input the PIC must be set up for EXTERNAL oscillator.  In that
configuration I thought that the OSC2 output was not active.  I do not
have a data book with me so check it out for yourself.  I would like to
hear about your results.


Martin Kirk
Arizona State University
(602) 263-9270

1995\07\14@093846 by Kalle Pihlajasaari

{Quote hidden}

The 16C57 does not have a specific external mode so I just put them into
HS mode (not selectable in the otp) and the inverter/occilator buffers
the signal
Kalle Pihlajasaari
Interface Products     Box 15775, Doornfontein, 2028, South Africa
+27 (11) 402-7750      Fax: +27 (11) 402-7751

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