most modern design for an HP41 rom module?

[MeindertKuipers]

(08-06-2024 07:12 PM)John Ioannidis Wrote:  Ah, that explains why I had used a bunch of BSS138 with pullups (like in the adafruit circuit I referenced) when I needed to go between 3.3V and 12V in a recent project. I'm so used to going from 5V to 3.3V, and occasionally down to 1.9V that I forgot about the upper limit

The BSS138 solution is quite well known and works in many applications. Problem is that these have pullups and the HP41 signals are all pulled down (except FI). For driving the HP41 bus I have also used the HCT125, which has an absolute maximum supply of 7V, which is just OK for the HP41. Anything rated up to 6V is not very suitable for HP41 interfacing.
For input from the HP41 system to a lower voltage system you could use a voltage divider, but this creates a constant load between supply and GND and could create a delay, so values have to be picked carefully. I will stick to the 4050/40109 combo, but it would be good to have an alternative and more compact solution, and one more input on the 4050 would be of great help.
And I do get my PCB's from JLCPCB as well, good service and quality. I have yet to experience their assembly service.