I have been thinking of building Ben Eater's 8 bit computer (on a budget) for some time now but the only EEPROMs I can find are serial EEPROMs with I2C interface. I am wondering if I can use a serial EEPROM as a parallel EEPROM. If so, How can I?

  • 1
    \$\begingroup\$ Write code to do it. Read and write from the I2C interface instead of a direct memory access. It will be very slow. \$\endgroup\$
    – Lior Bilia
    Commented Dec 21, 2022 at 14:22
  • \$\begingroup\$ Welcome. Do you mean the 2816 that's part of the output register? And the pair in the control logic? \$\endgroup\$
    – jonathanjo
    Commented Dec 21, 2022 at 14:23
  • \$\begingroup\$ Yes you can but it is so complex and slow that it is not feasible and you really don't want to do it. Don't use parallel EEPROMs then, use more modern chips like Flash. \$\endgroup\$
    – Justme
    Commented Dec 21, 2022 at 14:27
  • \$\begingroup\$ Why can't you use parallel flash (emulated eeprom)? Took me around 5 seconds to find a ton of such ICs. \$\endgroup\$
    – Lundin
    Commented Dec 21, 2022 at 14:28
  • \$\begingroup\$ @LiorBilia I think i will go with your approach for the control word, thanks \$\endgroup\$
    – zoomlogo
    Commented Dec 21, 2022 at 14:47

1 Answer 1


The two U47 and U52 are organised as a 1k x 16 bit ROM (A10 tied low). You might consider it cheating, but it's perfectly possible to program an ATmega328 as a 1k x 8 ROM. It sits looking at its input (address) lines, puts an appropriate byte out of 8 outputs. You see that chip enable and output enable both hard-wired active.

If you put it on a little circuit-board it would even be pin compatible! You could consider using their TX/RX and having some kind of RAM-based Eater CPU microcode.

You'll have to check clock speeds.

enter image description here
From Eater web site

In fact, if you look at the A7 address lines, they're tied high and low. (Are the two ROMs programmed with the same content, half used for each?)

U45 appears to be a seven-segment decoder or similar. Consider using a dedicated part for that if you don't want a third ATmega.

enter image description here
From Eater web site


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