Gigatron Hackers

Instead of feeding the shift register you could also add a parallel input to your Gigatron. Use a 74HCT574 or 374 octal flipflop and connect its outputs to BUS0..7. Clock (pin 11) goes to SER_LATCH (/VSYNC). Cut the /IE signal where it enters U39/74HCT595 at pin 13 and insert a three-pin jumper here...

Up only: 74xx461, 463, 590, 591, 592, 593
Up and down: 74xx469, 579, 869, 867

74HC(T)590 should be the most common one.

74HC393 is a ripple counter, like the 4040. Better use a 74HC163.

There is a Dutch company selling kits: https://www.budgetronics.eu/en/building ... a-25779-20

Neither works.. The scope shows that it is oscillating, but the output voltage is very low. The propagation delay of these is about the same as the 74C04 according to the specification, but I doubt that would be the problem, as I see it oscillating nicely. Did you try to change the bias resistor? E...

National Semicoductor's MM74C series has been introduced in 1976. So you could try a 74C04 instead of the '90s 74HCT04. However, it has 50 ns propagation delay and might be at its limit at 6.25 MHz. The CD4069A from the very first 4k CMOS series is even older. -A is the unbuffered configuration, wit...

USB keyboards from the transition time, when PS/2 was still common, often support both protocols. Newer ones do not. If your USB keyboard came with a green PS/2 adapter it should work. If no adapter was included it is unlikely that this protocol has been implemented.

So the first thing to do is to wire up the RPi's GPIO header to a female DB9 connector. You will need some sort of multi-conductor cable with at least 4 unique wires, (I would personally use a strip of ribbon cable for testing purposes and then clean it up later once it's running). Be careful, the ...

This is the access time rating. You will need 150ns or faster. So all three versions should work.

You should use 74HCU04 for an oscillator, not 74HC04. A 74HC04 actually consists of three inverters in a row, therefore it cannot be biased into linear mode (that's what the 1Meg resistor does).