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May 17, 2014

I laid out this circuit to use a cd4021 as the output shift register. I left an extra footprint on the board because I’d like to use a 74165 instead(the 4021 tops out around 2mhz which translates to the 1802 having to insert an dummy instruction between writes to the shift register). I laid it out with the 4021 out of caution but i’m pretty sure the 74165 will be fine so i might build it that way to start. The only signal difference is that the 74165 loads on a LOW pulse while the 4021 loads on high which i take directly from N1. I have spare gates on the 74c02 and one of the 74c00’s so that’s ok.  Also, the 74165 has a  clock inhibit pin which has to be tied low.
14-05-17 4021 to 74165

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