Cosmic wrote on 2022-04-26, 15:40:

But before getting that far I cannot get either port to pass a loopback test. I took some spare header cables and shorted two together, then connected them to pins 2 and 3 on the board. Pins 2 and 3 are always RX and TX under RS-232 and by shorting them together you should be able to see any characters typed locally, like a local echo.

That would depend on the flow control settings.

There was a FIC board I did "15 rounds" with back in the 90s as regards serial port functionality.... and with the onboard disabled and an ISA multi i/o with only the serial enabled it STILL wouldn't work. Narrowed it down to a BIOS issue in the end, but on that particular board, it did not have a flashable chip, and I hadn't come across hot swapping then, nor in fact did teh interwebs have many useful suggestions or resources for coping with it back then either. So that board went to the scrap/spares box, unsure if it survived the house moves since and will turn up.

weedeewee wrote on 2022-04-26, 15:46:

That would depend on the flow control settings.

Unfortunately no change between using Xon/Xoff or No Flow Control within Tera Term. :/

BitWrangler wrote on 2022-04-26, 17:00:

There was a FIC board I did "15 rounds" with back in the 90s

Certainly feels that way with this board, it's been a struggle ever since I got it. :D

BitWrangler wrote on 2022-04-26, 17:00:

Narrowed it down to a BIOS issue in the end

This helped me notice an issue. The sticker on the board says it's revision 1.2A E-O037 but the BIOS version is 1.15JE37, so the BIOS isn't for this revision. I found a bunch of BIOS files for this board online, I'll give one a try. I can't boot with the 1MB onboard cache enabled either so it would be nice if it's the same issue.

Edit: Nevermind, according to the release notes for the current BIOS, it says 1.15 even though it's for 1.2 boards:

1Model VA-503+
2PCB 1.2A
3BIOS Maker AWARD
4Version 1.15JE37
5Released 1999/8/26
6Flash flash73.exe

http://cwcyrix.duckdns.org/ftp-archives/ftp.f … /socket7/va-503+/

BIOS updated to latest (JE4333) but no change. I put a multimeter between transmit (pin 3) and signal ground (pin 5) and got +11.18V. I think it's supposed to be -12V when not sending. Holding down a key does lower it to about +10.89V. Without an oscilloscope I don't think I can learn more about what's going on, but the voltages definitely don't seem right. Maybe the UART is bad on this board.

Here's a good source I used in case anyone needs to look later:

https://tldp.org/HOWTO/Serial-HOWTO-19.html#ss19.1

You could always hook it up to another pc with a known working serial port.
Seems like transmit is working, the voltage depends on the key being sent.
You can always take out the board and start tracing which pin is connected to which pin, starting with the connector, going to the 75232, and going further to the W83877TF.

I tested the pinout from my FIC VA-503+ cable. I hope this helps.
Edit: My FIC VA-503+ is revision 1.2A

aitotat wrote on 2022-04-28, 13:24:

I tested the pinout from my FIC VA-503+ cable. I hope this helps.
Edit: My FIC VA-503+ is revision 1.2A
FICserial.jpg

Well, that could indicate OP is been using the wrong one all this time 😀
typical

aitotat wrote on 2022-04-28, 13:24:

I tested the pinout from my FIC VA-503+ cable. I hope this helps.
Edit: My FIC VA-503+ is revision 1.2A
FICserial.jpg

Good job ! I have a 503+ with original working cables and was going to pull it out but no need now 😁