DIP40 PCB for TT07: what about a breakout like this? about z80-open-silicon

[urish]

For project selection, you may want to go with something like the PY32F002A instead of the ATtiny?

Cheaper and the footprint is also smaller (QFN-16), if I'm not mistaken

[rejunity]

This looks great! Thank you and fingers crossed it fits in DIP40 sized PCB!

NOTE, I just realised one issue with my MUX approach combined with ZX Spectrum and frequency multiplier. The clock that is passed to Z80 on ZX Spectrum can be abruptly varying!
In "normal" circumstances Z80 gets 3.5 MHz clock (derived from PAL frequency) HOWEVER in case of memory contention between the video (ULA) and CPU - ULA wins and temporarily pauses Z80 clock. I assume that would cause an issue with U8 multiplier, right?

For example see:

See pin 32 from ULA (IC1) feeding into pin 6 of Z80 (IC2).

So, I am thinking, maybe it is better to have 2 clock inputs in TT design - one clock to drive internal Z80 core and another (higher) to drive internal multiplexor? In case of ZX Spectrum higher clock could come directly from 14 MHz crystal oscillator instead of multiplier.

[psychogenic]

Hm, I'm not actually seeing where the 3.5MHz clock actually comes from, but the interrupted clock--with no extra signaling just an abrupt hold--does look problematic... Will try and ponder.
As for the PY32F002A: it's small, and damn cheap. The MCU selection was preliminary--just wanted something cheap that could use an internal clock and have enough flash on board to play, and I like the AVR 2 series stuff. I also really like datasheets I can actually read.

[rejunity]

Hm, I'm not actually seeing where the 3.5MHz clock actually comes from

I added some annotation, ZX Spectrum's ULA creates an interrupted 3.5MHz signal to drive Z80 based on 14MHz crystal: