MCO as OSC_IN? How many other STM32 chips can an MCO line drive? Does daisy chaining work?

[bobert]

Posted on July 30, 2016 at 21:06

I need to run 32 stm32 mcu's on a single board.  Do I need a crystal for each or can I just use the MCO line of the top level chip for each, or do a 32 chip MCO daisy chain?

In a daisy chain is everyone on the same cycle all the time or is there any phase shift?Thanks

[waclawek.jan]

Posted on July 30, 2016 at 23:15

> How many other STM32 chips can an MCO line drive?

This is something you should be able to tell from the IO characteristics given in datasheet. Add the track capacitances and a pinch of engineering margin. > Does daisy chaining work? Why shouldn't.

> I need to run 32 stm32 mcu's on a single board.  Do I need a crystal for each or can I just use the MCO line of the top level chip for each, or do a 32 chip MCO daisy chain?

Or can you go just with the HSI? Or throw in a couple of dedicated buffers? > In a daisy chain is everyone on the same cycle all the time or is there any phase shift? Any phase shift there always is. JW

[Tesla DeLorean]

Posted on July 31, 2016 at 02:24

I think the term would be ''fan-out'', a daisy-chain would seem to infer you stuff the signal in the HSE, and pull a new version out of MCO, and so on along the line, which is clearly going to given you a phase shift as it enters/exits each domain.

Fanning out to 32 other chips seems a bit optimistic. You'd probably want to have a couple of tiers of buffers, and uniform line lengths so you don't skew