Reverse-engineering the 1977 Unisonic 21 calculator/game (part 4.5)

Hooray! I threw together an LTSpice simulation of the clock circuit from part 4, and it does what I thought it did!

sim_clock2.jpg

"OUT", the upper trace, is the Y1 signal. I was particularly interested to find out what happens at the gate of M5 when M1 is off, which is when P012 is high:

sim_clock2_node.jpg

That's interesting! It does remain low when M1's gate is high (so M1 is off), although it does rise up a few hundred millivolts depending on whether P14 is high or low.

In any case, simulating small parts of the chip like this is useful. It also gives confidence that if I make a printed circuit board for the circuit, it should work, barring some unforeseen integration issues.

The progress map now. Note that the unmarked section in the middle right is just interconnections.

progress_clock_gen2.jpg