smaller HP 82166A with 32-pin connector

[Klaus Overhage]

   
   
In the manual for the PANAME ROM there is a chapter about plotters, which deals with operating devices from other manufacturers with the help of the HP 82166A on the HP-41. The last 18 pages of this booklet
http://www.jeffcalc.hp41.eu/divers/files/jpc-15.pdf
describe how you can use the Canon X-710 without PANAME ROM. However, it remains unclear exactly how the plotter was connected to the HP 82166A. And so I tried it out myself.

I bought a Canon X-710 in the original box with all the accessories that were included at the time and shown in the manual. A CANON <-> CENTRONICS interface was not included. Then I built an adapter from the HP-82165 to the Canon printer with the help of the PIN assignment from this page https://gtello.pagesperso-orange.fr/cx07_e.htm. The same PIN assignment is also shown in the manual for the BASIC-Computer X-07. A KODAK Diconix 180si connected to this HP-82165 using a self-made cable works fine. I can print on it from the HP-41CX immediately after switching it on. This won't work with the Canon X-710. It does its self-test without any problems and prints all characters in the process, but it doesn't receive anything from the HP-41CX.

Then I tried to control the X-710 by hand using 8 switches for the 8 bits and a button for the strobe signal. This brought two important findings: First, if a printable character is present, it is printed immediately with Strobe without waiting for a carrier return or line feed. With all switches on high, i.e. 255, the plotter does not react at all. Second, contrary to the current standard, the X-710 only reacts to the change from low to high of the strobe signal. The Strobe signal is high when idle and the computer briefly sets it to low to indicate that a byte is ready.

Actually, this byte should also be available some time before and after the strobe, but the HP 82165 as well as the HP 82166A switch the 8 data lines to high resistance (TRISTATE) immediately after setting the strobe line high again, which is read by the X-710 as 255. Inverting the strobe line did not help either, nor did an extension of the DAVO signal with the help of registers R02 and R03 of the HP devices.

With an old 2-channel oscilloscope, I was able to track the temporal relationships and also see that the X-710 briefly sets its BUSY output to high to confirm the data transfer. I have come to the conclusion that the X-710 needs more time to take over the data after the strobe. With the help of the circuitry shown above from the two IC'S 74HCT573 and 4069, the data byte is now buffered. The STROBE signal goes directly to the plotter and is inverted for the LE input of the 74HCT573 using the 4069.

The BUSY output of the plotter goes directly to the RDYI input of the HP-82166A. However, the X-710 cannot pull the RDYI input to low. I had to install a 1k Ohm resistor from RDYI to GND so that the BUSY signal was recognized. The 5V supply voltage for the two ICs and the HP 82166A is generated by a WINOMO LM2596S LM2577S DC-DC converter from the battery voltage (6.2V) provided by the X-710.

Now everything works, as the linked video shows.
https://www.dropbox.com/s/n359qnu6ypsnus...M.mp4?dl=0

I wonder what kind of interface the author of the French article used back then. He writes:
"En fouillant plus a fond dans la boite; nous decouvrons un petit sac
contenant: une interface CANON <-> CENTRONICS, permettent le branchement a
un convertisseur HPIL lui meme relie a une la boucle HPIL."
That means translated:
"By digging deeper into the box; we discover a small bag containing: a CANON <-> CENTRONICS interface, allow connection to an HPIL converter itself is connected to the HPIL loop."

I don't think there was such an accessory from CANON. So who built it and how did it work?