Clocking

[Brian Cockburn]

Has anyone thought about using the Si5351 clock generator driven by a small Arduino like thing for retro CPU designs?  I envisage it being used to generate the master baud rate clock (1.8432 MHz or similar) and an adjustable main CPU clock.  The CPU clock would adjust with a rotary encoder - maybe 100 kHz to 20 MHz in 100 kHz steps.  The most recent frequency that was set would be written to EEPROM and recalled at reset to get the generator going ASAP.  There's a third clock channel for 'something else' too  (VGA clock at 25.175 MHz ??).

Adafruit do a board: https://learn.adafruit.com/adafruit-si5351-clock-generator-breakout/overview

AliExpress have many: https://www.aliexpress.com/w/wholesale-Si5351-Clock-Generator.html

Here's a bit of a project: https://pu2clr.github.io/SI5351/

I think for this sort of application it would need an output to hold the CPU in RESET until the clocks were running then release, and off we go.  No need to assert RESET again, even if changing frequencies.  Although a 'Restart the Clocks & CPU' button might not be a bad idea.

[Dave White]

I'd never considered this, but I've just ordered a few modules from AliExpress to have a play.

[Phil G]

Interesting, for a recent project I've recently been looking at glitch-free software-selectable clock rate multiplexing and programmable oscillators like the LTC69xx series, so this is up my street atm...