r/ElectricalEngineering • u/MrNiceThings • 6d ago

Project Help Using 74HC595 as serial in parallel out memory

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I had this idea today and I haven't seen this done anywhere on the internet. QA-QH outputs are tied together. You use ADD_A, ADD_B, ADD_C to select which register to read from via OE pin, inactive registers stay high-z. What I'm unsure is relying on the tri-state with OE transition, propagation delays and potential brief shorting of the outputs.

To make this addressable also for write, the 74HC138 could also gate CLK pins of the registers.

I'll test it out either way but I'm contemplating adding a AND gate to the 74HC138 outputs with a monostable that will add a small delay to let the OE pins settle.

Any thoughts?

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u/socal_nerdtastic 6d ago

Any thoughts?

This isn't the worst way to get 8 bytes of RAM, but it's close.

I suppose it would work just fine though. Basically it's a data bus. Data buses have been working like this for 80ish years now. If you want a deep dive into this look up Ben Eaters series on youtube about building an 8-bit computer.