I would like to create a 20Mhz clock that generates a square wave for the home-brew Z80 computer I' making. I already have several 20MHz crystal oscillators but am at a loss when it comes to circuit diagrams and other components needed. I have looked around but I haven't found any diagrams with all of the details that I need.


  • 1
    \$\begingroup\$ Are you sure your Z80 can run at 20MHz? The fastest version I am aware of was Z80H, which ran at 8MHz max. \$\endgroup\$ – jippie May 8 '14 at 18:52
  • \$\begingroup\$ The one I bought is in fact the 20MHz model \$\endgroup\$ – VivaDaylight3 May 8 '14 at 19:02
  • \$\begingroup\$ @jippie it goes up to 25 MHz; see the end of this page z80.info/z80brief.htm \$\endgroup\$ – Cornelius May 8 '14 at 19:13
  • \$\begingroup\$ @Cornelius I wasn't aware of those advances. Last time I checked the Z80 datasheets there was no such thing as SMD or QFP and I thought development was discontinued after the 8MHz version. \$\endgroup\$ – jippie May 8 '14 at 19:20
  • \$\begingroup\$ @jippie neither did I, but I found it in that link. \$\endgroup\$ – Cornelius May 8 '14 at 19:21

You will need a 74 series IC (7400, 7404, 7406 etc.), two capacitors and two resistors.

Here is one possible circuit for a square wave clock generator:

enter image description here

Source: z80.info by Thomas Scherrer. Also check his site for more Z80 related information.


If you have a crystal oscillator (they usually come in a 4-pin can), you just have to apply power (and ground) to the oscillator, and it will produce a 20 MHz square wave, which can be fed directly into the Z80's clock input.

If you have a plain crystal (usually in a 2-pin can), the other answers show possible oscillator circuits.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.