HP-IL with HP 82163A Video Interface

[murphy9]

(12-15-2023 02:33 PM)MeindertKuipers Wrote:  

(12-15-2023 10:00 AM)MeindertKuipers Wrote:  Just be aware that the FET level shifters may not work the way you expect with the HP41. Input to your Pico setup is probably OK, but I doubt if this will correctly drive the bus for the required ISA, DATA and FI outputs.

I did a quick test as I planned to use the same FET based level shifter. It works fine for active low signals which are an output from the HP41 (for the HP41 this is only the FI line which I am using it for). The FET level shifter have pullup resistors, most of the HP41 signals are active high, so need to be low most of the time. The pullups will interfere with this. You could use a resistor network for input the the RP2040 as a poor mans level shifter.
Best is to use a CMOS 4050 for downsifting, and a CMOS 40109 for upshifting.

Thanks - interesting I'll do some more homework before I connect to the 41c itself.