View Full Version : Multiple Propeller - one oscillator

Brian Riley
10-13-2006, 01:27 AM
Somebody else talked about this before but I am not sure I am clear on the matter. If I want to run a group of say 4 Propellers chips, I can take a 5.000 MHz clock oscillator can and put its single ended output to XI on the first propeller chip (let's call it P1), then attach the XO from P1 to the XI of P2. Now what do I do next run the same line to XI of P3 and P4, or daisy chain it XO of P2 to XI of P3, XO of P3 to XI of P4. What do I do with any unused XO pins? terminate them? Ground them? Pull them up?

Now in doing this am I garunteeing that each chip will be running exactly in phase with each other chip?


cheers ... brian riley, n1bq, underhill center, vermont
See the K107 Serial LCD Controller at
www.wulfden.org/k107/ (http://www.wulfden.org/k107/)

10-13-2006, 01:36 AM
It seems you could hook up the crystal to the first Propeller's XI and XO pins, and set it for XTAL1 mode. Then, wire that Propeller's XO pin to the other Propellers' XI pins, and set them for XINPUT mode. You might need to go to XTAL2 mode on the first Propeller to get the voltage swing to reliably trigger the other two chips' XI pins. As far as the unused XO's go, just let them float.

The "safe" way to do something like is to use an oscillator and drive it straight into everyone's XI pin (and set them for XINPUT mode). That way, you're assured adequate drive level and phase coherency.

You could enable all chips' PLL's in either case.


Chip Gracey
Parallax, Inc.

10-13-2006, 01:50 AM
The advise of Beau in this thread http://forums.parallax.com/forums/default.aspx?f=25&m=147768 was to have a counter in one prop generate an external clocks for the others. Will cost you a pin, but sure takes care of potential wire loading and noise problems.

Nico Hattink