You're _way_ better at this than I am.
I've probably just had more experience. I started out life as a hardware guy...
Questions to help me understand the magic:
1. You'd mentioned SN74LVCH8T245 bus transceiver / level shifter chips.
You did this circuit with SN74LV244APWR instead because the address
lines are always outputs, and the data always inputs, and you don't need
bidirectional translation, right?
Correct (and I just copied it from the C64 project).
2. You only have pull-ups on the address lines. This is because the
outputs need to be lifted, but for the inputs, the '244 chips are 5V
tolerant?
3. You don't have pull-ups on A8 and A9, Mode 6, or COS. Pretty sure I
don't understand this.
Both of those are Syntor X weirdnesses and something we missed in the
legacy Xcat, there are pullups on A0->A7 in the Syntor X code plug but
not on A8, A9. Maybe it's an F8 thing.
4. We're getting 3V3 from the RPi?
Yes, there's a regulator on the Pico, I'm kind of assuming there's
enough head room to be able to power our level translators (and it's
also something I "borrowed" from the C64 project).
5. The 'LV244 doesn't seem to be available in DIP?
I haven't gotten into the physical aspects of the board yet. DIPs are
getting rare, The larger surface mount parts aren't all that hard to
solder, but certainly changing out parts for buildability is something
to look at before Dave starts laying out the board.
Thanks for all of your effort!
This is the first schematic I've done in years ... it was fun learning
a bit of Kicad.
Thanks for looking!
73's Skip WB6YMH
De
