A new design of the megabit adapter for U36 in the C128
I tried to recreate the original Megabit adapter for the U36 socket in the C128. The information to this project I found on cmb8bit.com. You can find the PDFs and the ROM binary file in the cmb8bit.com directory.
I designed a PCB with the information of the PDFs and tested the soldered PCB.
Unfortunately it does not work :(
Thankfully a guy (Kinzi) from the great Forum64 helped me out by troubleshooting.
I scoped the signals and figured out, that the transistor I used was too slow to trigger the D-FF.
After that I tried logic gates - but this does not work either.
I figured out that there is a GLITCH on Pin12 of U3
The GLITCH triggered always the D-FF and so it does not work :( what a bummer ;(
Kinzi mentioned that the /CS signal from pin12 of U3 has to be synchronized with the 1MHz clock of the C128.
So I poked around with this variation and that was the success.
The solution is to use two 74HCT173 D-FF and one 74HCT14 INV - so the /CS signal from pin 12 of U3 gets synchronized with the system clock
and addresses the ROM. BINGO
Take a look into the C128 U36 adapter manual or into the SCHEMATIC for further information.
You can find a panelized GERBER file version and a single file version.
The panelized version should work for the most PCB manufacturer.
I ordered by JLCPCB.
For any questions (technical / experience), please use the issue tracking system of github.
Greetz
JDet