Dan,

That's the same question as, "Can I run two PICs (CMOS devices) off the same
xtal" that comes up all the time.

Yes.  If you are using an xtal, take into account that the second ("slave")
device has some capacitive input which must be subtracted from the capacitor
normally on the OSC2 pin.  (Yes, use OSC2 to drive the slave chip).

If your slave device has an OSC2 pin, you can connect it to a third device, etc.

You might want to allow for some resistors to prevent overdriving the next
stage, too.

Andy










D Lloyd <dan.lloyd@GB.ABB.COM> on 11/17/2000 08:25:31 AM

Please respond to pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU>








 To:      PICLIST@MITVMA.MIT.EDU

 cc:      (bcc: Andrew Kunz/TDI_NOTES)



 Subject: [PIC]: Using PIC oscillator output to drive
          divider?








Hi,

I would like to use the PIC oscillator pin (OSC1/2) to drive an external
divider as described by the bad ASCII art below

eg

g=gnd, x=Xtal, inv=internal inverter for HS/XT mode. There is a resistor
(or two) missing, potentially.

                               | PIC internal
g----| |---------------|-----   osc1
                 |             |      |
                X            |    INV
                 |             |      |
g----| |---------------|-----   osc2
                      |        |
                      |        |_______________
                      |
                      |____| 74HC4040N clk-->QE|_________|Seiko 7600 CLK

This is similar to the diagram given in the PIC application notes on the
page for crysal operation/capactor selection etc

Basically, I will be using the crystal to give a nice baud rate multiple
but I need to divide this to drive the clock of a Seiko 7600A.

What I need to know is will I be able to drive this CMOS divider direct
from the PIC oscillator pins or do I need to do some buffering inbetween? I
would prefer to not have the xtal frequency affected by this being
loaded......

I had thought about making an external clock generator (using an unbuffered
inverter and the clock crystal config shown) but why bother when that
effectively is the same as what is on the PIC?

Any help/suggestions, please?

Best regards,

Dan

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