3.3V logic with the ULA

[blittled]

I am planning on doing some experimenting with the Teensy 3.5 controlling the memory using BusRQ, BusACK and the control lines that may falsely trigger the ULA. The Teensy is 5 volt tolerant so inputs are not a concern but the output is 3.3V logic. Most 5V logic chips will trigger a high with a high from 3.3V logic. Is that true of the Z80 and the ULA?

[1024MAK]

I’m not totally sure about the ULA, but it is configured for its digital input pins to be TTL compatible. As a TTL logic high at an input is 2V or greater, both the ULA and the Z80 should be okay if the Teensy can manage to pull up to above 2V.

Note that the clock input pin on a Z80 is different and definitely will not work with these logic levels. And if you want to drive the Z80 /RESET line, it’s better to use an open collector NPN transistor.

Mark