Month: September 2021

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Troubleshooting serial terminal connections (VT Serial Terminal, VT132, Packet Radio TNCs) – part 2

In my previous post, I said I was going to test my two serial cables with every serial device I have to work out which combination worked and which didn’t to find out what the difference was. It didn’t take long to realize though that the DB25 to DB25 serial cable I have that I assumed was a null modem cable only worked with certain types of connections.

For example, it only worked with a VT terminal to a modem type device (in this case a PK-232 packet radio TNC), but not terminal to PC. In the first case that is a DTE to DCE type connection (which worked), whereas the second is DTE to DTE (which didn’t).

  • A DTE to DCE connection requires a straight through cable
  • A DTE to DTE requires a crossover connection (tx to rx, rx to rx)

This realization pretty much confirmed that the cable that was only working for DTE to DCE connectors was a straight through cable, and explained why it didn’t work elsewhere.

Long story short, I picked up a cheap null modem adapter that does the crossover for you, converting a straight through cable to a crossover:

From left to right:

  • USB serial dongle, connected to the Pi
  • DB9 to DB25 converter
  • DB25 to DB25 null model adapter
  • DB25 to DB25 straight through (converted to crossover with the null modem adapter)

And now I can successfully get a terminal logon to my Raspberry Pi:

To enable the serial terminal login via ttyUSB0, see this post.

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Enabling serial tty login to a Raspberry Pi

Depending on what Raspbian version you are running on your Pi, the approach for enabling a serial tty login via a VT terminal differs, but on current/recent versions you can enable by enabling and starting this systemd service (steps from this post, and here):

sudo systemctl enable serial-getty@ttyUSB0.service

and then:

sudo systemctl start serial-getty@ttyUSB0.service

This assumes you are using a USB serial dongle and that it’s connected as /dev/ttyUSB0. You can check by doing a ‘ls /dev/ttyUSB*’ before you connect your USB serial adapter and after to check what device your USB dongle appears as.

If you’re running an older version of Raspbian not using systemd, you can add a line to /etc/inittab to initialize getty as described here.

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Revisiting SunPCI driver install on Solaris 10

I’ve posted before on installing the SunPCI drivers on Solaris 10 but skipped a few steps. Sites to download the drivers are limited, but if you Google for the exact file name, you can find some locations, search for SUNWspci3.tar.Z

Unzip the file with:

uncompress *.Z

The untar with:

tar xf SUNWspci_13.tar

The SunPCI card in my Ultra60 is a 1.3 card, not 3, so be careful which package you download. Available options seem to be SUNWspci_13, SUNWspci2, SUNWspci3

Once you’ve untar’ed, run in the same folder:

pkgadd -d .

(not as I said before to cd into the untar’d folder). At this point you should be able to follow the rest of the steps in the previous post.

I’m reinstalling and setting up Solaris 10 on this box since I spent some time installing FreeBSD and then Solaris 8, and decided Solaris 10 was actually the better option, so I’m going that to that again (Solaris 8 I couldn’t get to install).

At some point I must have mounted a shared drive on my NAS to copy files to/from this box, so I’ll also take a look at getting that going again (I don’t think I took any notes), I could have used ftp. Will see what works.

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Troubleshooting serial terminal connections (VT Serial Terminal, VT132, Packet Radio TNCs)

I’ve been on a serial terminal kick the last few months. I think it started when I picked up a used Sun Ultra 60 and found out you could boot with a serial terminal to diagnose boot issues, and/or logon via a serial terminal. I built a VT132 kit and this has worked well using a regular VGA monitor and USB keyboard, but one thing lead to another and I started shopping ebay for a real DEC VT terminal. These are getting harder to find in working condition and it seems the prices are going up to pretty crazy levels. You can easily get one around $200 to $300, but if you shop around you should be able to get one around $100.

I’ve been able to connect the VT132 to anything so far and get it to work. There are a couple of jumpers on the board to select a straight through or crossover cable connection, if one doesn’t work change it to the other and it will connect. I’ve used it so far to connect to a AEA PK-232 Amateur Radio packet TNC, my Ultra 60, and a PC running Ubuntu.

The VT terminal on the other hand is more tricky. It will connect to the PK-232 and the wifi modem on the VT132, but I have not been able to successfully connect it to do a serial terminal logon to a Raspberry Pi (this was my main goal), or another PC yet.

My suspicion is that the 2 serial cables I have that I’ve been using interchangeably depending on what I’ve connecting too just based on the connectors are not the same. One has DB25 to DB25, the other has DB9 to DB25, so I’ve been picking the one that connects between the two devices. I’ve assumed these are both null modem cables, but I think one is straight through, and I don’t know which is which. I need to test them with a meter to find out.

I also thought the USB to serial connector that I was using on the Raspberry Pi was not working (it was a FTDI chip) so I bought another one using the Prolific chip, and that didn’t work either connecting from the VT Terminal, but it did from the VT132, so I think this is more to do with the serial cable than the Serial USB adapter. I think the clue was that from the VT132 it only worked when I switched the straightthrough to crossover jumpers to crossover, actually the same setting that works with the Ultra 60 too (but not the PK-232).

My next steps are to create a table of all the combinations that work vs don’t work. I also need to test the cables to find out if one is a straight through vs the other being a crossover cable. I think assuming they were the same is not true and this is causing the confusion. I will keep you updated on my findings!

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