smaller HP 82166A with 32-pin connector

[Klaus Overhage]

I myself have no experience with the use of the GETO output. The GETO output is High in the idle state and is briefly lowered to low by the HP-41 TRIGGER command.

With my HP-82165A, high only means 3.9V. This is because all output lines within the HP 82165A that do not belong to the 16 data lines DA0-DA7 and DB0-DB7 are routed via a TTL IC with the name 74LS244.

This 74LS244 only has the task of protecting the output lines. Its two control inputs 1OE and 2OE (PIN 1 and 19) are connected to GND and thus the inputs are always switched through to the outputs. In my attempts with the Canon X-710 I think my HP-82165A would be defective because its DAVO = STROBE output only supplies 3.9V. Therefore I unsoldered the IC 74LS244, soldered in an IC socket and inserted a newly bought 74LS244. As a result, nothing has changed: DAVO and GETO ran 3.9V in the idle state. I find that strange, but I guess it's OK.

I ran this little program in the HP-41:
01 LBL TRI
02 LBL 01
03 TRIGGER
04 GTO 01
With my oscilloscope I could see that GETO changes from 3.9V to 0.2V for about 0.0007 seconds. In order to be able to do something with such a short pulse, you need an IC that can store it. For example two NAND gates as shown on page 155 of "Control the world with HP-IL".
https://www.friedmanarchives.com/Writing..._HP-IL.pdf

Or the set input of a 74LS74. Or a 74HC123 as described on page III.03 in the book "HP-41 Input / Output Board" and "IL2000 Interface System". You can also see this circuit on page 30 of the 3/1990 issue of PRISMA
https://de.calameo.com/read/00255147754c837634df9
https://calc.fjk.ch/bibliothek/prisma-zeitschriften/
The article continues on page 32 of the next issue 4/1990.