Odd circuitry around clock pin on YM3526 (Commodore SFX Sound Expander)

[bluejay]

I was looking at the schematics for the Commodore SFX sound expander to see what kind of hardware was inside of it and noticed this odd circuitry on the clock pin. The left half has 2 inverters, 2 resistors, and 2 capacitors. I'm not sure how this bit works exactly but I assume it's designed so you can hook up a 2 pin crystal oscillator when you only have one clock pin. I'd love to hear an explanation how this works though, and whether I can use a same or similar circuit with the clock pin on a MC6847. But what I'm truly mystified by are the two inverters on the right. What is the point of having 2 inverters in series?

[brain]

This is a classic "crystal into oscillator" circuit.  I could explain it, but others do much better than I

 

https://learnabout-electronics.org/Digital/dig51.php

 

https://electronics.stackexchange.com/questions/489785/2-pin-crystal-oscillator-crystal-oscillator-circuit-explanations

 

You can use the same circuit for any device that needs a "clock" input, not a crystal input (BTW, ICs that use a crystal input just put the left hand circuit on the IC itself.

 

The 2 inverters on the right "boost" the signal from the generator, which can't take a lot of load itself.  ONly 1 is needed, in my opinion, becausing inverting the clock won't change anything, so turning it right side up is unneeded, but maybe they had an extra gate and it was easiest to just put it in play.

 

[ChildOfCv]

I've seen dozens of variations on this, but they are all basically 2 inverters into a loop with timing components, sometimes followed by an output amplifier, but not always.  Here's the simplest one I've seen, which is used in many of the experiments of the old Radio Shack Science Fair 200 kit.

 

[bluejay]

Thanks a lot for explaining this; I'll definitely make use of this circuit. I'm assuming I can connect multiple ICs that want the same clock speed into one of this circuit?

Edited February 21, 2021 by bluejay

[emerson]

3 hours ago, bluejay said:

Thanks a lot for explaining this; I'll definitely make use of this circuit. I'm assuming I can connect multiple ICs that want the same clock speed into one of this circuit?

Yes, just make sure you do not exceed the drive/source current of the inverter. Sometimes for line drivers the datasheet will make it easy and explicitly state how many gates the output can drive.