Adding a vt100

[Carl Marbach]

I have connected a Vt420 via a USB-Serial connector. When I boot RSTS/e V7.0 the terminal displays gibberish. How do I set the right baud rate?

The VT420 acts like a VT100

Thanks

Carl

[Clem Cole]

Is the baud rate correct with the RPI?   This might help you.  Make sure that Linux can talk to it before you try to get RSTS to talk to it.

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[Anton Lavrentiev]

IIRC, RSTS v7 that comes in the systems.tgz package does not have any
terminals configured. So it's your Linux console that you're seeing
in VT420 and that outputs gibberish.
getty (the terminal manager) has a very nice feature that it can
change (downgrade) the terminal baud-rate every time it gets a BREAK
from the terminal.
By default your Linux console assumes 115200 baud, which is too fast
for VT420. BREAK (which is F5 or Ctrl-F5 on VT420) would let getty
know to reduce (half) the speed one tier at a time.
IIRC, VT420 can work at 19200, so you might need to use the BREAK key
a few times. To be compatible with older DEC systems, though, it's
better to use 9600 for the terminal.
The successful baud-rate negotiation is signified by the correct
"login:" prompt seen on your VT420. If the BREAK key is pressed too
many times, it will circularly revert to the baud-rate it started from
(and then you will need to keep pressing it again to come down to the
rate used by the terminal). So, do this one BREAK at a time, and give
it a second (or so) to react (remember, the BREAK is much longer than
a keypress, about 1/5 of a second, IIRC).
HTH

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[terry-...@glaver.org]

On Sunday, August 17, 2025 at 11:42:57 AM UTC-4 cmar...@marbachs.com wrote:

I have connected a Vt420 via a USB-Serial connector. When I boot RSTS/e V7.0 the terminal displays gibberish. How do I set the right baud rate?

 

That can get complicated because of the number of layers involved. On a real 11/70, RSTS/E is talking to a real multiplexor board. On the PiDP-11 it is talking to a part of the emulator that pretends to be a mutiplexor on that side, and pretends to have virtual (or real) terminals configured on the other side. So simh needs to know how to "run (virtual) cables" between the multiplexor and virtual (or real) terminals.

On RSTS/E 9.0 or later, you have DCL to set the terminal characteristics, like this:
set terminal kbh0:/permanent/noautobaud/nodialup/speed=9600/device_type=VT320

I don't remember how this was done before DCL, so I can't help with your 7.0 system. What we have here is RSTS/E telling the emulated multiplexor that it wants the speed set to 9600. simh then looks at its configuration, and if the terminal exists as a real device in the configuration file, it tells Linux to set the baud rate. Linux looks up the device type and sends an IOCTL to the driver

for that device. The driver will  respond with one of:
1) Done, all good

2) I can't do that

3) Some part of doing it, which may or may not accomplish anything.
Once al that happens, simh interprets the response, transforms it into a (hopefully appropriate) RSTS/E status code and reports that back to RSTS/E

Let me share the relevant parts of my boot.ini (for use with my "canned" RSTS/E V10.1 disk.) Note that I am using vh devices, you will likely want to use dz11 instead. My vh0 line appears in RSTS as KBH0: and KB17: - two different names for the same thing. In the "set terminal" command above I'm using the physical device name (KBH0:) because the assignments of physical devices to regular KBxx: 
devices can change - using the command on KBH0: ensures I'm talking to the correct place. I actually have a VT420 attached to that port and it works fine.

The first thing that comes out on (working) serial ports when RSTS/E finishes starting up is something along the lines of "RSTS/E is on the air". If you simply have a baud rate mismatch, that could display as gibberish and keyboard input ignored (possibly with echoing of incorrect characters).

;
; Set up the USB-to-serial ports on the RPi
set vh lines=16
set vh dhu
set vh nomodem
set vh enable
;
; Note that these are "shuffled" so the cabling matches the panel
attach vh line=0,connect=/dev/ttyUSB0
attach vh line=1,connect=/dev/ttyUSB1
attach vh line=2,connect=/dev/ttyUSB3
attach vh line=3,connect=/dev/ttyUSB2

At the boot prompt about starting timesharing (or just "Option?" on older RSTS/E versions), you can type "HA  LI" (HArdware LIst) at that prompt and RSTS will tell you what devices physically exist on the system. Note that at this point in booting, RSTS's INIT.SYS knows about nearly every possible PDP-11 controller, even ones that RSTS/E doesn't support (either because RSTS/E never had a driver for it, RSTS/E had a driver at one time but support was dropped, like RS03/04 fixed-head disks, or your RSTS/E monitor was built without the driver).

As you see, it gets complicated quickly. Poke around with the info I provided and I'll try to answer ASAP (I'm having surgery on the 19th, so there will be a delay in all of ny answers at that point).

[Johnny Billquist]

And just in case the question was about the terminal side, hit F4 (I
think it is), which gets you into SETUP (key might also be labelled
SETUP). From there select COMM, and then select baud rates. Should be
straight forward...
Also pay attention to parity, as if you have things mismatching, it can
cause partial garbage as well.

Johnny

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[Anton Lavrentiev]

> hit F4 (I think it is), which gets you into SETUP

VT200+ setups are on F3. F4 selects sessions in terminals that support them. F1 is xon/xoff, F2 is print, and F5 is break

HTH 

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[Johnny Billquist]

Ah, thanks for the reminder. My bad. :-)

Johnny

On 2025-08-17 22:45, Anton Lavrentiev wrote:
> > hit F4 (I think it is), which gets you into SETUP
>
> VT200+ setups are on F3. F4 selects sessions in terminals that support
> them. F1 is xon/xoff, F2 is print, and F5 is break
>
> HTH
>
> On Sun, Aug 17, 2025, 4:41 PM Johnny Billquist <b...@softjar.se
> <mailto:b...@softjar.se>> wrote:
>
> And just in case the question was about the terminal side, hit F4 (I
> think it is), which gets you into SETUP (key might also be labelled
> SETUP). From there select COMM, and then select baud rates. Should be
> straight forward...
> Also pay attention to parity, as if you have things mismatching, itcan
> cause partial garbage as well.
>
>    Johnny
>
> On 2025-08-17 21:43, terry-...@glaver.org

> <mailto:terry-...@glaver.org> wrote:
> > On Sunday, August 17, 2025 at 11:42:57 AM UTC-4

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[Neal G.]

Adding to what others have said.

In the boot.ini file, you can preset the serial communication parameters like this:

attach -V dz Line=5,Modem,Connect=ser0;9600-8N1

This sets up 9600 baud, 8 data bits, no parity bit, 1 stop bit.

Here I specified "Line=5" which leaves the first four lines as "simulated serial" over telnet, and line 5 is the physical serial connection on my system (2.11 BSD UNIX at the moment)

Also, rather than specifying the device directly as in "/dev/ttyUSB0", I used the SimH alias "ser0"

To determine what alias name exist, and to verify SImH can access the USB serial device; at the SimH prompt, type "show ser".

Like this:

     sim> show ser
     Serial devices:
          ser0   /dev/ttyUSB0

The "-V" parameter tells SimH to send a verification string to the serial device when it connects.

On your terminal, you'll see this:

     Connected to the PDP-11 simulator DZ device, line 0

Followed by any initial connection messages from RSTS or whatever OS you're running.

Hope this helps.

- Neal G.

[Carl Marbach]

You are right. This is frustrating.  I have:

The terminal (a VT420 in VT100 Mode and set for 9600 Baud) which is connected via a USB to Serial converter and which worked last year.

From the Raspian shell, I have tried:

1. booted the Pi

2. Sudo Raspi-config

3. enable login shell over serial

4. enabled serial port hardware

5. screen/dev/ttyusb0 9600

6. terminal still shows garbage

7. Tried: sudo getty -L 9600 /dev/ttyS0 vt100

8. no luck

To see if it's working:

systemctl status serial...@ttyS0.service

yeilds:

a bunch of stuff

what now????

[terry-...@glaver.org]

All the Raspberry OS needs to know is that there's a serial port attached,

which happens automatically. It looks like you are trying to set it up as a

Linux login rather than just an available serial port.

I don't think your serial commands are doing what you think they are. I

believe those commands are for the serial port that's part of the Pi itself

(at least on the Pi 5).

I'd suggest undoing all of that and just use something like 'cat bigfile > 

/dev/ttyUSB0' (or whatever the port is named). This should be a text file,

ideally big enough that you can cycle through baud rates on the terminal

while it is still being output.

That will test output to the terminal. Once you have that working, you can

do 'cat /dev/ttyUSB0' and what you type on the terminal should be output

properly to your session on the Pi.

[timr...@gmail.com]

One thing I do when I am not sure my VT terminal is working right or not is to plug it into my Linux box.  Or your Pi.  Then use "sudo dmesg" to find

out what device it is at.  It's usually /dev/ttyUSB0 on Linux.  And /dev/ttyACM0 maybe on Pi?  Don't remember.  I have seen both.  Then I start up

Minicom (or some other terminal software and connect to that device at the baud rate the terminal is set for.  Characters from the VT will echo to

Minicom and characters from Minicom will echo on the VT.  This at least lets me know the VT is working as sometimes it has sat unused for 

a long time.  Once you get there you know the device to use now too.  You should be able to attach to it in Simh and you can do a "show dev" I think to 

see what it sees. I know I have done this on my Pidp-8.  Never tried it to RSTS on my 11.

[Johnny Billquist]

First of all, don't make things so complicated. It makes it so hard to
troubleshoot.

Start of with *not* enabling logins, or setting things up with screen
and all kind of cruft. It makes more things happen, and things work in
other ways than you might think.

Instead do the following. Plug the serial adapter in via usb. Figure out
what device name it has.

Then use stty to check and change parameters on that device (see the
man-page for the exact way you specify which terminal line you want to
manipulate).
Once you have things looking right with stty, then do

echo "Hello world" > /dev/ttyusb0

(or whatever the device name is), and you should see that output. If
not, then we have very few components to troubleshoot.

Johnny

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