multiple oscilators or shared ?

[Quack]

Hi,

I have a PIC circuit, operating happily with 4 PIC's, all doing their
stuff, all running at 8mhz. Each one runs with its own Xtal.

I am working on a redesign of this circuit, and was wondering if i
could just share a single 8mhz Xtal between all pics ?

Is this good, bad, even possible ?

If so, how exactly would i share it ?

(the distance between each PIC is a few centimetres)

Thanks

Alex.

 

[Activ8]

Hi,

I have a PIC circuit, operating happily with 4 PIC's, all doing their
stuff, all running at 8mhz. Each one runs with its own Xtal.

I am working on a redesign of this circuit, and was wondering if i
could just share a single 8mhz Xtal between all pics ?

Is this good, bad, even possible ?

If so, how exactly would i share it ?

(the distance between each PIC is a few centimetres)

Thanks

Alex.

use the external osc circuit in the data sheet.

 

[MNQ]

Hi Alex,

You could try and use a buffer IC and split the clock that way. The loading
of four PICs might be too much for the one Xtal.

Naveed

 

[Scott Stephens]

I have a PIC circuit, operating happily with 4 PIC's, all doing their
stuff, all running at 8mhz. Each one runs with its own Xtal.

I am working on a redesign of this circuit, and was wondering if i
could just share a single 8mhz Xtal between all pics ?

Is this good, bad, even possible ?

Yes, it is good. Why pay more? At least on some of the old pics.

If so, how exactly would i share it ?

The xtal oscillator has an input and output, so one oscillator pin
drives the others input pin. See the F84 stepper controller at my web
site, I have 3 16F84's using one oscillator. Should probably use a
common reset too.

The new pic's with internal oscillators may have changed. Got to RTFM.

--
Scott

**********************************

DIY Piezo-Gyro, PCB Drill Bot & More Soon!

http://home.comcast.net/~scottxs/

**********************************

 

[Leon Heller]

Hi,

I have a PIC circuit, operating happily with 4 PIC's, all doing their
stuff, all running at 8mhz. Each one runs with its own Xtal.

I am working on a redesign of this circuit, and was wondering if i
could just share a single 8mhz Xtal between all pics ?

Is this good, bad, even possible ?

I've done something like that, but I had one PIC and four '2313 Atmel AVRs
on the same PCB. I think I used a 74HC04 buffer on the output of one AVR
oscillator feeding separate buffers, one for each of the other AVRs. The PIC
oscillator was too fast for the AVRs.

Leon

 

[Michael]

I've done something like that, but I had one PIC and four '2313 Atmel AVRs
on the same PCB. I think I used a 74HC04 buffer on the output of one AVR
oscillator feeding separate buffers, one for each of the other AVRs. The PIC
oscillator was too fast for the AVRs.

Leon

Timely query. My current project has two PIC16F628, each running at 4
MHz with its own xtal+C. Just yesterday I dumped one set of xtal+C,
built an osc with the other xtal and a buffer chip. Drive each 16F628
at pin 16 ONLY (RTFM re: external osc). Both PICs still set for XT
osc., just like when they had their own xtal.

 

[Activ8]

Timely query. My current project has two PIC16F628, each running at 4
MHz with its own xtal+C. Just yesterday I dumped one set of xtal+C,
built an osc with the other xtal and a buffer chip. Drive each 16F628
at pin 16 ONLY (RTFM re: external osc). Both PICs still set for XT
osc., just like when they had their own xtal.

Good deal. They *are* easy to clock. I can ugly bug the things with
huge leads - no clue why clock probs ever get posted to the list.
.... that other poster mentioned using OSC2 to drive other OSC1s...
I'm not surprised. I remember at least thinking about seeing how
much that output could drive *reliably*.