Terminals

[Gary Robertson]

Good evening Gents and Ladies,

I appreciate your previous help and i now have two PiDP-11 systems that now recognise each other. 

They also recognise Mim.

The issue I have now is that I cannot get the system to connect to terminals.

i would like to attach to the terminals as a login (rather than a pi and reboot pidp11)

i want to connect as I recall back in the 80's when I logged in as an engineer in a steelworks control room to monitor blast furnace parameters and loadings. 

Simple circles on a VT-240  showed temperature , CO, CO2, burden rate, all by a big room that was encased and had  a lucite, window, and you couldnt go in without showering.The PDP-11 was a thing of wonder for those who had no access,

Once I find my feet, I'd like to add some real ADC and DIO to PiDP11 for myself.

The place I refer to is the British Steel Plant - RavensCraig, Motherwell, Scotland

PDP11/70 and RL02 all over the place!!

anyway, enough,

any assistance on the VT520 issue is appreciated

 I have installed two USB to serial interfaces and wired as per "obsolescence guaranteed' instructions and I am having no success.

I have wired the consul terminal connections and as per , no activity.

I have a genuine VT520 terminal and it refuses to play.

alll assistance is appreciated

[Johnny Billquist]

Again - you need to tell us what OS you are using. I would possibly
guess RSX, since you mentioned they can connect to MIM (I assume that is
what you meant).

Beyond that, it would be helpful to know what your ini-file for your
pidp11 looks like, and I hope you have not tried to enable those serial
ports under Linux.

Johnny

> --
> You received this message because you are subscribed to the Google
> Groups "[PiDP-11]" group.
> To unsubscribe from this group and stop receiving emails from it, send
> an email to pidp-11+u...@googlegroups.com
> <mailto:pidp-11+u...@googlegroups.com>.
> To view this discussion visit https://groups.google.com/d/msgid/
> pidp-11/2b2d8a15-f264-400a-85ea-560788421dadn%40googlegroups.com
> <https://groups.google.com/d/msgid/pidp-11/2b2d8a15-
> f264-400a-85ea-560788421dadn%40googlegroups.com?
> utm_medium=email&utm_source=footer>.

--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: b...@softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol

[Perry Metzger]

On 3/13/26 17:20, 'Gary Robertson' via [PiDP-11] wrote:
> Good evening Gents and Ladies,
>
> I appreciate your previous help and i now have two PiDP-11 systems
> that now recognise each other.
>
> They also recognise Mim.
>
> The issue I have now is that I cannot get the system to connect to
> terminals.

In general, wiring up RS-232 or similar terminals used to be a way to
guarantee hair loss. You will want a good RS-232 breakout box to debug
such things when they fail. Luckily such things are not overly expensive.

Perry

[terri-...@glaver.org]

On Friday, March 13, 2026 at 5:20:07 PM UTC-4 gary.rob...@btinternet.com wrote:

 I have installed two USB to serial interfaces and wired as per "obsolescence guaranteed' instructions and I am having no success.

Which instructions, exactly? There are a number of iterations which seem to have lost information along the way.

Likely the easiest to start with is USB to 9-pin serial RS-232 cables - that way you don't have to fiddle with installing and cabling the optional RS-232 level shifters on the PiDP main board. You'll just need the appropriate adapters and gender changers to convert the DE-9 female on the cables to whatever you have coming out of your terminal(s).

These should appear as /dev/ttyUSBx (where x is a number) devices in ls /dev/ttyUSB* - for example:

pi@spcpi1-host:~ $ ls -l /dev/ttyUSB*
crw-rw---- 1 root dialout 188, 0 Feb 20 00:05 /dev/ttyUSB0
crw-rw---- 1 root dialout 188, 1 Feb 20 00:05 /dev/ttyUSB1
crw-rw---- 1 root dialout 188, 2 Feb 20 00:05 /dev/ttyUSB2
crw-rw---- 1 root dialout 188, 3 Feb 20 00:05 /dev/ttyUSB3

By default, the Raspberry Pi OS will not try to establish login sessions on these, leaving them free for SIMH to use.

In your SIMH config, you'll want something like:

;
; Set up the emulated DHU11 multiplexor
set vh lines=16
set vh dhu
set vh modem
set vh hangup
set vh enable
; Use Telnet port 4000 for non-physical ports
attach vh 4000
;
; Set up the USB-to-serial ports on the RPi
attach vh line=0,connect=/dev/ttyUSB0
attach vh line=1,connect=/dev/ttyUSB1
attach vh line=2,connect=/dev/ttyUSB2
attach vh line=3,connect=/dev/ttyUSB3

That is for a DHU11 multiplexor. Older operating systems may not support it, and you can use the DZ11 instead.

Just change all instances of "vh" to "dz", and comment out the few lines that will throw errors when you run that

script as they're vh-specific.

You now have a DHU11 or a DZ11 multiplexor with up to four ports "connected" to the PDP-11 operating system.
The rest of the 16 ports will give you a terminal session when you telnet to them from the Pi or another system.

I am using port 4000, but you can pick any non-reserved port you want.

Of course, the operating system needs to know what to do with them. You'll need to let us know which operating

system and version you want to use for system-specific setup info.

I have wired the consul terminal connections and as per , no activity.

When you say "console", are you using that as a generic term for a terminal port, or do you mean the actual oper-

ating system console? The operating system console is normally attached via the "screen" command on the Pi.

There are multiple options here, from running the Pi itself with a serial terminal, to using the Pi as usual and just

having the emulated operating system console on a serial port. None of these is easy to set up, and I'd suggest

leaving things as they are and just attaching your physical terminals to the emulated multiplexor ports as I show

above.

  

I have a genuine VT520 terminal and it refuses to play.

Even "back in the day", this stuff wasn't easy unless you ordered it all in one system from DEC. Once you started

making your own cables, etc. you needed some skills to get things going. And emulation doesn't make this any

easier - as I mentioned, just making the serial ports available to the emulated PDP-11 OS isn't enough - you need

to configure the OS appropriately.

Once you have the basics working, you can get fancy and wire up the RS-232 converters on the PiDP-11 board

and make cables. I'm attaching two views of what I did on my first PiDP-11 build. This is what Oscar used on

his web site, until most information was lost with only a picture remaining. The way I have things set up, the

ports on the back of the PiDP-11 are identical to the ports used on DEC systems, so standard DEC cables can

be used to attach terminals - I'm using VT420s, but all DEC terminals followed the same standard.

I apologize for the pictures being on top of each other (if indeed they are) - Google Groups is having one of its

pissy days and won't even let me delete them and retry.

[terri-...@glaver.org]

On Saturday, March 14, 2026 at 10:14:59 PM UTC-4 terri-...@glaver.org wrote:

I apologize for the pictures being on top of each other (if indeed they are) - Google Groups is having one of its

pissy days and won't even let me delete them and retry.

Actually, it decided to not insert them at all. Let's try that again...