VT100 VGA Not Working

[David H]

The VGA Term is displaying the copyright ... but not displaying the actual terminal output.

This was working at the very beginning, when I first assembled the boards.  I only used it once or twice, but now I'm unable to get the serial output on the VGA Term.

I may have inadvertently changed some settings, without realizing it. I've tried resetting everything I can think of to defaults (reloaded sd card contents, reset altairduino settings to defaults, reset vt100 settings to default, reflashed the Due with the precompiled binaries ... etc).  But I still can't get terminal output over VGA.

Both the USB Programming Port, and DB9 serial are working as expected ... as does the front panel.

All other aspects of the system also appear to be working as expected (audio, sd, etc).

Any suggestions?

[Chris Davis]

Make sure the SD card is inserted.  When you "raise SW0 and hold up DEPOSIT", that is indicating to the Arduino that it should load Configuration #1 from the SD card.  If you think you may have changed configuration #1, then you can download new contents for your SD card from the website: https://adwaterandstir.com/instructions/

[Chris Davis]

You can also try to manually change output to pins 18/19 (https://adwaterandstir.com/2017/06/03/serial-device/, or read David's original documentation). 

[David H]

I've reset the sd card contents to the files found in disks.zip linked from https://adwaterandstir.com/instructions/, I've also reset the Altair settings to defaults, and the VT100 to default settings 

This did not resolve the issue

[David H]

I tried this, I get nothing on the vt100 vga output when I try to manually set the configuration to use it on pin 18/19 following those instructions.

[Chris Davis]

Make sure the activity indicator flashes when you press a key on the keyboard.

Check continuity from D18 and D19 on the Arduino to pins 5 and 4 on the PIC32.

[David H]

i have continuity, and the led blinks when I press keys on the keyboard

[Chris Davis]

So the Altair-Duino is turned off.  You set SW0 up and all other switches down.  You raise DEPOSIT (and hold it), then turn the power switch on, and release DEPOSIT.  VGA screen displays the copyright.

Then what do you do?

[David H]

all switches down, and then AUX1 down ... to try and get a listing of options ... this works with both USB Serial and RS232 

[Chris Davis]

Does the activity LED flash rapidly when you lower AUX1?

[David H]

no

[David H]

I am able to load things like CP/M off the SD Card as well - so the SD card is functional, and does not appear to be corrupt 

[Chris Davis]

I'm pretty much running out of ideas here.  If I had that here, I'd connect an oscilloscope to D18 and D19 and see if any data is getting to the PIC32.

[Mark Cohen]

Happened to me. I received 2 bad SD card adapters. You can tell it's bad if the metal part can pull away from the little PCB. Both the original and replacement right out of the electrostatic bag had the front pads not connected to the PCB. It therefore can't read the SD card so stops.

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[David H]

Mark, as mentioned - the sd card appears to be functioning properly as I’m able to load CP/M, Basic, and various other items off of it

[Chris Davis]

One last long shot - are you sure SW0 is working? Flip it up and toggle EXAMINE and see if the LED above it illuminates. Also verify DEPOSIT is working.

[David H]

examine and deposit switches are working 

[Chris Davis]

And SW0?

[David H]

I hooked up a logic analyzer to D18/D19 via the the "Pro Expansion Conn" on the front panel pcb (IO Bus board disconnected), and nothing ... I also hooked up my scope, and see no data - I started Altair the same as always, SW0 Up, Holding Deposit ... wait a moment, then press AUX1 down a few times while checking the scope ... I also put triggers on D18 and D19 in my logic analyzer and saw no change

D19 sits high (~3V), D18 sits low

D18 also appears to have continuity to GND when checking with my DMM

SW0 also works, sorry, I meant to confirm that in the last message as well - apologies.

I'm going to remove the front panel and inspect the soldering ... though I've already done this, ... but I'm going to check again.

[David H]

Interesting, possibly ... I don't know much about the Due ... but D18 is not shorted to ground on the front panel pcb when I remove the Due ... 

But when I check the Due itself, D18 is shorted to GND on the Due board when it's removed from the PCB.

[Chris Davis]

D18 definitely should not be shorted to GND.  Sounds like something happened to your Arduino.

[David H]

What are my options here? It worked once or twice, at the very beginning ... and then stopped working shortly after ... 

Any ideas on how D18 got grounded ... everything else works as expected ... just a bad Due?

[John Galt]

what about using usb connection to terminal software, going into the configuration and overwriting profile #0 so that it uses the VGA VT100 by default. 

this way on power up it defaults to profile #0 with the VT100 and there is no selecting switches. if you want to undo in the future just revert the SD card DAT file.

this why it bypasses a bad sw0 if that is the issue.

then you can also setup the default drives in the config menu and save that so on power up it also bypasses the front panel switches if that is the problem.

you can then just go into configuration mode and swap disks that way instead of flipping switches.

[Chris Davis]

I can't say what happened.  I've never seen this in more than seven years of making this kit.  I would guess something happened to the Due, like some kind of short.

[John Galt]

unless there has been a solder blob or something was not fully soldered and over time it just went from marginal to not connected.

my idea is since the issue is the terminal mapping, then set it inside the configuration to automatically switch on power up and maybe bypass a defect. 

this is because the altair can be accessed via external terminal allowing access.

if the configuration change allows the vt100 built in terminal to work then it can help trace what is going wrong.

now on my kits i have experienced weirdness with the switches when the machine sits for a long time. i had the switches not read properly because i would guess there is oxidation inside.

so what i do now from time to time is i cycle all the switches up and down a few times, and i use DEOXIT and i drop some inside the switches from the front, it serves 2 purposes 

1) lubricate the switches since they can stick a little

2) help any oxidization with a little DEOXIT that gets into the switch

plus i exercise the switches trying to keep the contacts clean.

i treat my machine a little different in that i make all my changes inside the configuration menu and save them to profile 0.

thus i rarely use the front switches, just makes things easier at the cost of a little less originality.

could it still be a bad SD or Due yeah, but if you can work around in the short term why not plus it can help pin point what is defective.

if the issue is SW0 it would also cause issues with selecting a disk to load.

doesn't the new firmware also have a front panel and switch test?

its amazing how non-related things can also cause problems.

i just had a USB 3.5 disk drive cause some kind of noise that interfered with a WIFI card on the same machine.
makes no sense but you just roll with it.

[da...@hansels.net]

This sounds like a Due with a broken D18 pin to me (no idea what would have caused this). D18 is the serial
output that (in the AD) goes to the VT100 terminal. Even if the software is misconfigured it should float high,
not shorted to ground. As a final confirmation test I would suggest to do the following.

Take the Arduino Due out of the AD (powered off) and measure directly on the Arduino between D18 and GND.
If that is a short then D18 is toast. If not then upload the following code to the Due (via the Arduino IDE)

#define PIN 18

void setup() { pinMode(PIN, OUTPUT); }

void loop()  { digitalWrite(PIN, HIGH); delay(1000); digitalWrite(PIN,LOW); delay(1000);  }

That should give you a 1-second-high (3.3V), 1-second-low (0V) output on pin 18 which can be easily
measured with a Voltmeter. You can double-check by using a different pin (changing "#define PIN 18").

If that works then it's probably a software problem after all. Re-upload the AD firmware by following
Chris' instructions. Maybe the re-upload helps in that case.

[David H]

dhansel - I’ve already confirmed the Due has Pin 18 shorted to ground by removing it and testing it directly.

There are no shorts on the Altair PCB’s with the Due removed either.

With the Due removed, on its own, powered off… d18 has continuity to Gnd.

Seems like the only logical next step is to test with a known good Due, but as they are quite expensive … I’m likely going to just give up at this point.

Rs232 works, as does usb serial… so I’ll probably just use my VersaTerm for when I want the VGA terminal experience.

I’m unsure if I should cut a trace on the Due, or on the Altair front panel to disconnect d18 all together… not sure if this short is or will cause problems in the future.

[da...@hansels.net]

Ok I wasn't clear on whether you had measured the Due directly. Sounds like D18 is gone.

I don't think you need to cut any wires on the AD. The VT100 should not have a problem with

the RX input being constantly low (other than not receiving any data).

If you feel a bit adventurous you have one more possible way to continue. There are two unused

(sort-of) pins on the Arduino Due that can be converted into an extra serial port for the AD.

Take a look at page 10 of my Documentation. That describes how to enable the extra serial
port (you will need to modify your Arduino Due for this as shown).

So you could do the following:
1) enable the extra serial port as described (requires re-uploading the AD firmware)

2) cut the traces on the AD circuit board that connect D18 and D19 to the internal VT100 terminal

3) add wired from the extra serial port RX/TX to the VT100 terminal

4) in the AD configuration, change the "Primary host serial" setting from "Serial (pin 18/19)" to "Serial (RXL/TXL)".

That would restore the AD to full functionality without extra cost. It's probably easier to just 

use the RS232 output with VersaTerm but it might be an interesting project.

[Chris Davis]

That's a good idea David,  Actually the pre-compiled binary at https://adwaterandstir.com/install/ has the RX/TX LED Serial port enabled, and I believe the SD card image available from https://adwaterandstir.com/instructions/ has the RX/TX LED configuration saved as config #3.

[David H]

thank you both for all the help diagnosing this issue - I think I'm just going to live without the VGA Term working for now ... I do have a VersaTerm I use for various other projects, and that works well with the Altair over RS232

I may eventually try the RX/TX LED hack ... I did buy some ESP-01's I was hoping to eventually use for wireless serial ... I assume the RX/TX LED hack would lock me into using either the VGA Term or the ESP-01's ... when it comes to this, I'll probably just buy another Due ... 

Though I am still confused as to how D18 was damaged ... outside of just being a defective board?

[John Galt]

I have my setup using rx and tx I have a fabgl ansi terminal using that port.

It’s more capable than the Geoff terminal.

So you end up with an extra usable serial port on gx/rx you have your sd card and you have your port b 9 pin.

This could be a gift horse for you. Just ending up with an extra usable serial port.

Look over your due board top and bottom maybe it’s a stray solder blob from original construction or a bad joint you can fix.

Worst case it is just a defective due.

[Chris Davis]

I have purchased and programmed more than 2500 Dues and have only seen two bad ones.  If they're bad, they're bad from the start, if they're good they keep working.  Kind of like Newton's first law, paraphrased: an Arduino Due that works keeps working unless acted upon by an outside force.  They don't have issues that pop up after a while.  So who knows - an unseen solder bridge or an accidental tap across connections with a screwdriver.

[Han Neko]

This is super interesting!

I built my Alter-Duino back in the dark days of 2022. The VGA terminal never worked, it never got past the "ASCII Video Terminal Ver 1.3" message. It never bothered me much but today something came over me and I thought I would take a look at why. After some troubleshooting and googling about I found this thread with the exact same issue with the exact same pin. My D18 is also connected to ground with the Arduino disconnected. I followed the trace under magnification through a few vias from pin 18 to the pin on the Atmel. I couldn't see a misplaced blob of solder or anything that could be causing it. I reflowed both pin D18 and the pin and its neighbors on the Atmel. This didn't fix it. My guess would be a bad microcontroller.

It is interesting that both OP's Arduino and my own suffered the same exact fate. I forget if this Arduino came with the kit or not. Knowing me I bought a used one from ebay and the previous owner fried it somehow. I wonder if plugging in rs232 directly would do that?

Either way, I ordered another used one from ebay. Will that one also have a dead D18? =D

[Han Neko]

My new-to-me Due arrived today. A quick check shoes that D18 is not tied to ground. I am happy to report that my VGA console is now fixed and working!

[John Galt]

YIPPY!

hey now everyone with the same issue can suspect the DUE is defective.

[David H]

Thanks for confirming I'm not the only one - makes me feel a bit less crazy, :)

I have a Due clone coming from Alie, no clue how "legit" it is ... was only likr $18 ... ordered it along with some other supplies I needed for a different project ... will eventually try it out in the Altair and see if it resolves the VGA issue ... for now, I'm just going to hook up my VersaTerm to the RS232 serial when I want to use my VGA display with it.

On Wednesday, June 5, 2024 at 4:10:37 PM UTC-4 han.po...@gmail.com wrote:

[Chris Davis]

If it's a blue clone, it should just replace your current Due after programming.  If it's a black clone (the Due-CH340), you may have to remove the 47uF capacitor that is above it on the main PCB.