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I recently purchased an old Wyse WY-55 dumb terminal on a whim, and I've been experimenting with different things I can do with it. I wanted to try hooking up the terminal to a NetBSD machine. I figured it would be pretty simple since NetBSD is among the most "Unix-y" of the modern Unix-likes, and it should still have good support for these types of serial terminals. As it turns out, the process *is* simple. The main complicating factor was that the computer I run NetBSD on does not have a serial port, so I had to use a USB serial adapter. Figuring out how to get NetBSD to communicate via the USB adapter wasn't very hard either, but I figured I would still document the process in case someone finds it interesting or useful.
The FTDI-based USB serial adapter is nothing special; I just bought one of the first ones I found. NetBSD has a fine FTDI driver, so the adapter worked out-of-the-box for me.
The null-modem cable allows two devices with serial connections to talk to one another directly without a modem in between. The cable I bought also adapts the 9-pin connection on the RS-232 adapter to the 25-pin serial connection on the terminal.
The main thing to make sure of is that you actually have a null-modem cable. A null-modem cable has the transmit pin on one end wired to the receive pin on the other end, and vice versa. The handshake lines may also be crossed. See here:
Some reviews said the pins on the Cables To Go null-modem cable were wired incorrectly. However, I believe those users were either trying to use a null-modem cable for something it is not designed to do, or they were misunderstanding the pinouts of the DE-9 and DB-25 connectors. In my experience, the Cables To Go null-modem cable *is* correct and it works for its intended purpose, but do your own research.
The USB serial adapter plugs in to the computer USB port and to the null-modem cable. Then the null-modem cable plugs into the "modem" port on the terminal.
Here are the settings I used on my WY-55. You may be able to get things to work with other settings, but here is what I used:
There are many more settings than this, but the above are the ones I specifically set. Certainly not all of them are necessary. I'm still reading the WY-55 manual and experimenting to figure out what everything does.
I knew that NetBSD would use a device node to talk to the terminal, but I wasn't sure which one. When unsure of what device node gets used to communicate with a device, it's often a good idea to check the system messages. After plugging in the USB serial adapter and running `dmesg`, I saw the following log:
uftdi0 at uhub3 port 3 configuration 1 interface 0 uftdi0: FTDI (0x0403) USB Serial Converter (0x6001), rev 2.00/6.00, addr 1 ucom0 at uftdi0 portno 0
The first thing to note is that NetBSD recognized the device immediately and correctly attached it with the USB FTDI driver. Also notice that it says something about `ucom0`. At this point I searched the /dev directory for any device with `ucom` in it but did not find any. However, I figured there might be information in the man pages, so I ran `man 4 ucom`.
The ucom man page says that it is associated with two device files:
/dev/dtyU? and /dev/ttyU?. The ttyU? devices are used for dial-in, and dtyU? devices are used for dial-out. The dial-out device file was the one I needed to start a connection with the terminal.
Once one knows what device file to dial-out to the terminal with, connecting to the terminal is quite simple (a very similar process should work on the other BSDs also). I opened /etc/ttys and added the following line:
dtyU0 "/usr/libexec/getty std.9600" vt100 on
The /etc/ttys file is read by init(8). For each device listed that has the `on` flag, init will run the specified command.
The first column says what device file to use. In this case, it's dtyU0, the "zeroth" dial-out device file that the USB serial adpater is associated with (the device file I found reading the man pages). The second column is the command to run. The `getty` command will initialize the terminal and show a login prompt. The `std.9600` argument sets the baud rate to 9600, which is what I have my terminal set at. The third column is the terminal type. I have it set to vt100 (and the WY-55 is in vt100 emulation mode) for simplicity. Then the last entries are flags. The `on` flag tells init to run the command. You can also have a `secure` flag here. That will allow root login on this terminal. I didn't want to enable that in this case.
After saving my changes, I ran the following command to restart init and have it re-read the /etc/ttys file:
kill -HUP 1
Voila! A login prompt on the WY-55 terminal!
From there, I could use the serial terminal as intended.
Another nice thing is that on restart, if the USB serial adapter is connected, init(8) will initialize the terminal and send a login prompt to it as part of its normal process, now that there is an entry for the device in the /etc/ttys file. If I want to turn that off, I can just set the flag for the device to "off" in /etc/ttys.
