Here are some Screenshots from the Scope
I've probed pins 1 to 20 with the device running "normally" directly after startup.
Pin 8 is the RD-Pin, which tells the connected P8279 that a data-read is requested. Pin 10 is WR, telling the 8279 that there's data incoming.
Upon startup I can see a short pulse on WR, after which the front display starts to flash the first digit - All digits display 0 at this time (see this Video:
https://youtu.be/Q0UMYOMQdPU ). Once a key is pressed, the Square-Wave LED lights up fully, while the Sine-Wave LED lights up at about half power and the triangle-wave LED glows very dim. At the same time, the Digits go crazy. From that point forward, nothing else happens.
This happens with every keystroke and is only stopped by power-cycling the entire device.
Interestingly, once this failure-state is reached, the Interrupt-Line is constantly low and there's a bit more ripple-voltage on the supply-rails.
First Screenie is Pin 8 - RD
Second one is Pin 10 - WR
Third one is Pin 11 - Address Latch Enable - As you can see, the amplitude is not constant, which I find very odd
Fourth one is Pin 14 - One of the Data-Lines of the Bi-Directional bus. It more or less looks the same on the other data-lines, except for pin 15, where I could see no signal (measurement-error or there's really no signal in that mode, idk.)
Edit:
Little note to the previous post: The SRAM-Circuit I built uses a Zener-Diode instead of the 2 white LEDs to turn on the Transistor when the Programmer increases the VPP-Voltage from 5V to the programming-Voltage.