Hey! many thanks to all. Geez this list is great! I did'nt even have time to repost my first request that I already had 3 answers... ________________________________ Tobie Horswill Ex Machina, Quibec (Quibec) CANADA thorswil@exmachina.qc.ca ----- Original Message ----- From: "Spehro Pefhany" To: Sent: Thursday, August 16, 2001 10:22 AM Subject: Re: Multiple uCs sharing same clock > At 09:32 AM 8/16/01 -0400, you wrote: > >Hi, I was wondering if there were any quirks that I should know of if I want > >to drive several PICs from the same clock ? A 20MHz ceramic resonator in > >this particular case. Can I simply run all the PICs clock inputs in parallel > >on the same resonator ? Somehow this doesn't feel wright, perhaps I should > >"regenerate" the clock at TTL level first ? I recall a circuit that did > >something like this on the MicroChip site but couldn't track it down... > > If there is much distance (more than an inch or two with ground plane) > between the clock pins, it might be wise to buffer the clock output pin > using a single gate buffer. Here is one possbility, most of the > manufacturers have something similar: > > http://www.fairchildsemi.com/ds/NC/NC7S32.pdf > > One input to the clock OUT pin from the PIC with the crystal, decrease > the capacitor value by the input capacitance of the 7S32, and connect the > other input of the S32 to 0V. The output of the gate drives the other > PIC(s) using the external clock circuit (clock OUT open, input to clock IN). > > If you have the room, a 74HC32 will be a bit cheaper (0.19 vs. 0.39 US/100pcs) > > Or, use a packaged oscillator, which is guaranteed to work, as someone just > mentioned. > > Best regards, > =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- = > Spehro Pefhany --"it's the network..." "The Journey is the reward" > speff@interlog.com Info for manufacturers: http://www.trexon.com > Embedded software/hardware/analog Info for designers: http://www.speff.com > Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com > =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- = > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics