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cedws | 2 years ago

Could this be used to build a super minimalistic Ben Eater style CPU?

discuss

order

dusted|2 years ago

Yes, however, it's best suited for the complex parts (logic that needs a lot of inputs and few outputs) due to the fact that the eeproms it generates data for are arranged as 8 bit output.

It might also be somewhat slow compared to discrete gates, the AT27C512 I'm using is rated at 45ns access time, while a normal DIP gate is usually around 5.

That said, 45 ns, means it should function up to about 20 mhz if I'm not totally wrong (which I've been known to be before).

I made this because I need some logic for my DEC J-11 CPU and to keep it period-ish-correct didn't want to bring in an fpga, I'll use it for power-up settings and controlling memory bus access. I could have used a PLA or GAL, but I don't have any and I have about a kilogram of the beautiful old quartz window EEPROMs :)

kjs3|2 years ago

it generates data for are arranged as 8 bit output

There were/are x4 proms (e.g. am27s10 == 256x4).

45 ns, means it should function up to about 20 mhz

Theoretically. If you're careful.

I need some logic for my DEC J-11 CPU

Cool...I keep wanting to do something with my J-11s beyond play with ODT. What are you doing for storage? That seems to be the problem with most PDP-11 projects...most of the available OSes are deeply tied to storage related DECisms.

RetroTechie|2 years ago

> and I have about a kilogram of the beautiful old quartz window EEPROMs :)

You mean UV erasable EPROMs (window = for letting the UV in).

EEPROMs are erased electrically and thus don't have a window.

royjacobs|2 years ago

It can function as a NAND gate, and anything can be built out of NAND gates. At that point it might be simpler to just use actual NAND gates though :)

dusted|2 years ago

Definitely, if you just need some nand gates, this is probably the worst way of doing it, where it can be of some use is when you want to describe more complex behavior, where you quickly end up with a mix of tens, hundreds or thousands of gates.