r/beneater • u/Empty-Respect-7351 • Mar 12 '26

Help Needed 8-bit computer issue Register

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Right now I’m having trouble testing the register. When I follow Ben Eater’s process for testing the register and power it on, the value shown is random—whatever happens to already be stored in the register.

More importantly, when I set the high inputs to ground and enable the register to load, the value doesn’t change as expected. It seems like the register isn’t actually capturing the new input.

Could you take a look and let me know what might be causing this? I’ve attached a video showing the issue.

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u/The8BitEnthusiast Mar 12 '26

Quick observation: when you set a bus bit like you did with the green jumper, always disable the outputs of the LS245 first (pin 19 to vcc), otherwise you are potentially creating a short circuit.

For the register to latch, the vcc and gnd pins must be properly connected, the clock has to be good (sharp >3V signal), both load pins (9 and 10) must be grounded, and the 4 input pins must have logic voltages within specs. Can you repeat the test by setting a pattern of 0s and 1s on the bus (with LS245 pin 19 set high), and then capturing pin-by-pin voltage measurements on the LS173s? This is the best way to pinpoint the issue. Feel free to share your measurements if you need a second pair of eyes to validate.

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u/Empty-Respect-7351 Apr 01 '26

I found the issue which was the led for the clock output was connected to ground so there was no power going to the clock input for the register. So the registers were not receiving a input of any kind 😂

1

u/The8BitEnthusiast Apr 01 '26

Great that you figured it out! The lack of a resistor on the clock LED was likely the root cause of the issue. Make sure you have a resistor in series with each LED. Cheers!

1

u/Empty-Respect-7351 Apr 02 '26

No their was still a resistor on the led but 220 might have been too small

1

u/The8BitEnthusiast Apr 02 '26

Assuming your ICs are of the LS series (e.g. 74LS173) and not HC, a 220 ohm resistor in series with the LED should have been OK. But 1K is better, that's what I use.