I was hoping to demonstrate the H9 terminal on my “pioneer” setup (ca. 1977/78) at VCF. This would have been the heathkit terminal offering at the time (assuming you couldn’t afford an LA-36 DECwriter!).
I have my mostly “restored” H9 from last winter
https://photos.app.goo.gl/c35iwjgdYuwrbzVRA
but I’m having trouble with serial communication. I have tentatively diagnosed this as some kind of loading issue on the serial port, but I’m certainly no expert. I am trying to use this with the H8-5 serial port (which was the normal configuration at the time).
I have it set for EIA (RS-232) output and have checked all of the jumper configurations and believe I’m in sync with the manuals.
Here are three traces of the signal, all showing the letter ASCII “K”. the first trace was taken with nothing connected to the terminal:
https://photos.app.goo.gl/vdj13p6mYfmNTZQ4A
the signal reaches +10.1V for “Space” (Logic 0) and -11.3V for “Mark” (Logic 1). Looks good.
When I connect the terminal (via null modem) to my PC and run TeraTerm I see the following trace:
https://photos.app.goo.gl/owRKz4B2hRnbg5h89
The “Space” level is pulled down now to +4.9V, but that is still within EIA specs and I am able to communicate two ways between the TeraTerm window and the H9. Note however I must set my TeraTerm configuration to 7 bits, no parity, one stop to get this to work. This is odd because the I/O board in the H9 is definitely jumpered for 8-bit operation, but as I look at the waveform indeed it appears to NOT be sending the most significant bit. For reference here’s what a “K” should look like:
https://upload.wikimedia.org/wikipedia/commons/b/b0/Rs232_oscilloscope_trace.svg
note in my traces the MSB “0” is missing?
Anyway, for the final trace here is what happens when the H9 is connected to the H8 via the H-8-5 serial port:
https://photos.app.goo.gl/pVEbgiL285oAijky6
note that the “Space” level is now only +2.5V, which is below spec (must be between 3 and 25). Using the simple test procedure in the H -8-5 manual I get random jibberish when I try and read from the port. Also HDOS boots fail because I can’t even send the “B” for Boot!
FYI here is what the output section of the H9 looks like:
https://photos.app.goo.gl/KsSWJjoctiwU32oc6
Does anyone have any thoughts on this or have you possibly experienced this? It looks like one could play with the resistor values to control the voltage levels? But why should I have to? the board is built to original specs?
I have actually tried this with two different H9 I/O boards (same results) and three H-8-5 boards. Do the LEDs in the 4N26s degrade in output over time? (they would all have to have degraded because I’ve tried many boards.)
I’m stumped…
One possibility is to set the H9 to TTL output mode and then put TTL-to-EIA driver chips in, but that’s probably not something I would put on my plate now.
Tx for any thoughts/input… if I can’t get this to work I probably won’t bother lugging it to VCF…
On Sep 28, 2021, at 10:03 PM, glenn.f...@gmail.com wrote:
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Change jumper to use position 1-3 to use 1K resistor instead for pull-up.
Norberto
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Norberto, Joe: thanks for the suggestions!.
The H9 is now working! But it turns out that the RS232 level thing was a red herring. I went back and carefully examined the cabling. I was using Heath-supplied cables to connect the H8 and H9 but perhaps one of the cables was originally wired for a different configuration? (DECwriter?). the standard cabling requires three connections (Rx, Tx and GND) but this cable had a fourth connector installed. It turns out that was providing a spurious input which worked its way all the way to the UART on the H-8-5.
Removing the mysterious fourth connection solved the problem and the H9 is now working. The keyboard shroud must be installed just right or the keys bind on that so I’ll have to look at that. Also I have some kind of “ghost” cursor on the screen but I think I’ve narrowed that down to a handful of chips on one of the boards.
Anyway we’re “go” for the H9, which will make this a much more authentic “pioneer” (1977/78) exhibit.
I’ll post pictures soon.
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You were quite the “boy genius!”
I have an H9 from Ed Aumiller (“rescue” last summer). I think he did every upgrade imaginable on this thing but it’s a rats nest of wire wrap and point-to-point solder patches. Not sure I’ll ever get that working. but I think he did the 24 line mod and upper/lower case. Looks like maybe an auto-repeat circuit. But the stuff is all just hanging loose in the chassis. If I ever work it it would be to try and restore the original functionality. I did turn it on and I think the CRT and high voltage power are good so it would probably mostly be a matter of debugging the digital electronics. Maybe if it’s a long winter…
The keyboard on this thing is heavily worn. It was apparently a real workhorse back in the day…
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