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KimH · 03-14-2021, 06:44 PM

OK - It's raining... Again.

Hi Klaus or anyone ready to help

I know this may be a bit mundane - please be gentle. I have a couple of questions which you may be able to help me (and others) with

As the 82166A devices (I have a handful) are known to be a bit sensitive AND not replaceable, I got myself a 82165A GPIO "in a box" - it seems to be built a bit more robust/resilient and has its own 5V Power-Supply which you can tap into for experiments. I learned that in Control the World with HP-IL, which is my inspiration for getting started,.

The idea is that once I had done the same experiment as you have done using the same book and Circuit, I would move to the 166's and start doing some real I/O (Bi-directional, ADC/DAC, Optocouplers etc) - Read Christopher Klug, Interloop 211 et all

I got the components - Inverter & Latch - and a nice Canon 25 D-Sub plug with a "breakout-box" for the connector on the 82165A and got going, using the 5V power rail from the 165A.

It did not work as expected, it seemed like the 473 was in saturation mode with the nice LEDs (used blue ones). I simply couldn't get the LEDs to look as I had hoped for.

Several iterations and I realize a couple of things.
- The Latch was indeed stressed, it did flash the LEDs but VERY briefly
- The Inverter was working, but not triggering the LE, it appeared (but it actually did)
- The latch seemed to not be Latching...

So thinking Saturation I stopped using the 5V Power from 165A and put a separate PSU to feed the 74HC chips & LEDs. Which actually worked wonders... @3.8 Volts. Actually all the way from 2,5 volts it worked - LEDs behaved as expected.

Thinking I had lost my wits I tried to work my way back up to 5V. I was putting the 100, 220 (that one value would be right) and even 1k Ohm in series with the LEDs, not much of a change, the voltage divider/current limitation just would not play along as hoped for, current kept flowing in abundance, voltage controlled by the LEDs.

So here is the question/suspicion. Does it matter if I use the 74HC (CMOS) or the HCT (CMOS TTL-Level) - this may be the issue... Can anyone here give a hint?

BTW: The 74HC574 does not require the Inverter on LE (vs. 373 & 473), one chip saved Smile

(09-16-2019 07:23 AM)Klaus Overhage Wrote: Thank you for your explanations. Then this device is probably not so strange and could work. It already has the same MCU as the production unit. But the ICs are still rotated as in your prototype. That explains probably the strongly deviating PIN assignment of my variant compared to the technical manual. The name is displayed by the HP-41CX with CCD module in Catalog 0 as HP82166A.

In the meantime, I was able to build the simple circuit from the book "Control the world with HP-IL", page 42. Instead of a 74C373, a 74HCT573 is used. The tests, whether so 8 LEDs can be switched were all positive. The DA0-DA7, DAVO, RDYI, DACI, + 5V and GND connections are all correct. The "Count" program on page 44 ran to 255 in 96 seconds. With the HP-71B, a flickering light looks very pretty.

Code:

10 RESTORE IO 20 A=DEVADDR("%64") 30 ENDLINE "" 40 X=1 50 FOR I=1 TO 8 60 OUTPUT :A; CHR$(X) 70 X=2*X 80 NEXT I 90 FOR I=1 TO 8 100 OUTPUT :A; CHR$(X) 110 X=X/2 120 NEXT I 130 GOTO 50 140 END