mega65 / mega65-r3-expansion-board Goto Github PK

Footprint pinout has different pin ordering to the C64 pin numbering.

The footprint pin numbers and the C64 pin number that they correspond to:
FP 6 - C64 7 ***
FP 1 - C64 1
FP 4 - C64 4
FP 2 - C64 2
FP 8 - C64 6 ***
FP 7 - C64 8 ***
FP 3 - C64 3
FP 5 - C64 5

So only pins 6, 7 and 8 are wrong.
We have 8 = +5V, which is C64 CHROMA
We have 7 = Not Connected, which is C64 +5V
We have 6 = CHROMA, which is C64 Not Connected.

Until this is fixed, I will need a special "incorrect" cable to make the hook-up

Move H10 10mm right.
Move H7 1mm right.
Move H9 0.25mm up and right.

Pin 10 is the input, and pin 9 is the output, not the other way around

At least 0.1" is required. Much more may not be possible.
Not socketing those chips would help with vertical clearance.
Alternative is to place them elsewhere on the board, if space can be found that is routable.

Not critical, but it would make the fit more comfortable.

Confirm estimated difference and fix. Probably another 0.5mm further apart between the two PMOD pairs. But that's just an estimate.
The boards do fit together, it's just hard to put it all together.

It's possible to fit both a tape drive plug and a USB connector through the tape port cut-out, so we should allow this.

1. TE0790 to the left of H8
2. TEI0004 behind H8
3. TE0790 relay somewhere, to allow connection to the MEGA65 main board. Perhaps in front of H8

1. 74HC165 can handle up to 7V, but only 50mA from inputs being driven above their current Vcc.
2. 74LS595s that we are using to drive outputs will drive a nominal 5V/100Ohm = 50mA, which is already borderline.
3. Any connected device driving the lines will further increase the current into the 74HC165. Therefore we need current limiting resistors.
4. 1K or similar would be fine.

Board will require a fair bit of re-routing to fit these resistors in, but it should be possible.

For testing with revA boards, we flying close to the wire with 50mA drive strength being pushed into them will probably be ok. To test 100% safely, can cut the traces on the PCB and add blue bodge wire to resistors.
Otherwise it will be time for lots of bent pins on ICs or maybe I will just make a nice little adapter board that does the required work. There is space to the right of each of the 3x 74LVC165s if I made an adaptor board.

... and add thermal relief to GND and 3.3V pins?

... probably easier to move it on the bridge board. Whichever board requires a respin can have the correction.