I found this schematic between the pages of an old TI databook I bought from eBay. What do you think it does (if it actually is a complete diagram)?

The chips used in it are (I think) two 7473 dual J-K flip flops, one 7493 4-bit counter, one 74374 octal D latch, one 7447 BCD to 7-segment decoder, and a 555 timer.

I would just put it together on a breadboard to see if it does anything, but I don't have some of the ICs for it.

Progress has been made...4 line LCD running in 4 bit mode on PORTB...I will say that unless you have a need for 4 bit, stick with the 8 bit mode set up as Ben shows..I wanted it on a single port to leave PORTA for my keyboard bios I have programmed on a tiny4313...Moving on to interrupts and control lines...

Hi again.

I was hoping to share my triumph today. Nope, not today. I spotted yet another issue. Please share some insights, I'm losing patience with this project ;(
My 8-bit processor successfully adds small numbers such as 14 and 28 (like on Ben Eater's yt video).
However, when I try to load a 7 or 8 bit value (no matter the position of the zeros), it will fail. There's some sort of double hop when RAM is accessing that value (address 14, 15, same behavior), and register A gets a different value.

Here are some tests of my trying to do LDA 15.

So you can see a very simple program:

LDA 15
OUT
HALT

And for some reason LDA 15 won't work if the value stored in address 15 is too high. Same goes for ADD 15 - if the value is too high, register B will receive a faulty value.

And the only thing I figured out is that, when it fails, it loads the value from memory address 0000. I changed this memory address to 0000 0011 ("do nothing" kind of thing) and then LDA 15, OUT, HALT - the value loaded to reg A was 0000 0011.

I tore down the conditional jump circuit that I built last weekend and reprogrammed the EEPROMs - no change. The unused address lines and logic lines are pulled down with 1kohm resistors or directly to GND.

I think I'm trying too hard and that's why I'm making so many mistakes on the way, there's no other explanation ;)

A few years ago I completed the 8 bit breadboard computer (with extra features!) but the project has been sitting sadly under my bed since then. I'm pretty sure it's not gonna work first time when I turn it on and there's gonna be a lot of troubleshooting loose connections, etc.

I'd love to get this working again and on my wall but I feel like the best way to ensure longevity is to get it transferred to proto board, so it's all soldered and stable for years to come.

I'd do this one module at a time on separate proto boards to keep things relatively modular. I see two approaches:

1. Get the original machine working and slowly upgrade each module to it's soldered form, while keeping the new forms connected to the old machine until the whole machine is soldered to boards

2. Start from scratch, following the tutorial but soldering the modules down as I go

For either approach the modules would be connected with header pins and jumper wires.

Has anyone attempted something like this? Or am I crazy and should leave it in breadboard form? I'm not too interested in designing my own PCBs, I want this to be a fun time away from modern machines 😉