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Sharing a clock between ICs

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2camjohn

Member
I want to share a clock between a couple of ICs.

Lots of places talk about sharing clocks but I cant find any schematics which actually show the implementation.

My friend Mr google isnt helping much.

I guess its one of these things thats assumed to be so simple nobody goes into details about it.


Anyway, hopefully the MS Paint schematic I have attached is not too offensive.

My questions are:
Will the way I suggested work?
Is there a better way?
Any other tips?

Links to websites resources where they cover sharing clocks between devices would be immensely helpful.
 

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MrDEB

Well-Known Member
is this what you mean by shared clock circuit?

basic method depending on IC's.
 

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mneary

New Member
The website you need to check is the website for the chips you are hooking up. MrDEB has given you the solution to problems 1, 2, and 3 below.

1) Most chips do not like to have a load on their OSCOUT pin, while others may tolerate this.

2) Most OSCIN pins are not sensitive enough to take the OSCOUT signal from just any other chip.

3) Although some chips will function as a buffer from OSCIN to OSCOUT, this is an extremely uncommon hookup for reasons 1 and 2.
 

georgetwo

Member
following the 1 and 2 rules, it is also possible to share oscillator. feed the osc output to other osc input with transistors or not gates. I mean the oscout can feed transistors biased as notgates. in that case, the output of the osc will not be affected by load.
 

mneary

New Member
following the 1 and 2 rules, it is also possible to share oscillator. feed the osc output to other osc input with transistors or not gates. I mean the oscout can feed transistors biased as notgates. in that case, the output of the osc will not be affected by load.
The transistor NOT gate cannot have zero load; you just hope it's not enough to disturb the oscillator.

The OSCOUT signal isn't usually a valid logic level, as this consumes a lot of power that's not necessary. The data sheets won't tell you what the levels are.

By the time you have converted the unknown OSCOUT signal to a stable logic level, you have used a lot of parts. IMO you're better off reading the data sheet and following MrDEB's advice. You should only use the OSCOUT signal if the data sheet says you can.

Of course you're always free to ignore the spec, if you don't expect any support. It's easy design something that usually works.
 

Mikebits

Well-Known Member
Just to add a few more tidbits. Clock distribution is usually done as shown in attached image. I like to use source and shunt terminations to clean up signal quality. Trace length is also important. Clock lines are critical signals and most care should be given to these lines. Daisy chain, do not use star configuration. See my image.
 

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