Updated: Using TTOX with a USB USB Serial Port

[Mike Katz]

I am trying to connect a USB serial port as a device at address 41 in the simulated PDP-8.

When I try attach ttox0 /dev/usbTTY0  or any other /dev/tty device SIMH says "unit is unattachable".

I also tried attach ttox line=0, connect=/dev/ttyUSB0 and that also produced the unit is unattachable message.

show serial outputs the following:

 ser0   /dev/ttyUSB0

If I try attach ttox line=0,Connect=ser0 that give the same message.

Once I get it attached how do I set the baud rate and format (110-8P2 for the teletype)

My goal is to use my ASR33 to punch binary tapes and text tapes as an output only device and not on the console.

As an additional comment the show and help TTOX commands are not all supported like they are for TTOX.

sim> show ttix lines
lines=4
sim> show ttox lines
%SIM-ERROR: TTOX device: Non-existent parameter: LINES
sim> show ttix summary
0 current connections
sim> show ttox summary
%SIM-ERROR: TTOX device: Non-existent parameter: SUMMARY
sim> show ttix connections
all disconnected
sim> show ttox connections
%SIM-ERROR: TTOX device: Non-existent parameter: CONNECTIONS

Thank you David Gesswein for getting me this far.

Some information also came from:  https://simh.trailing-edge.narkive.com/BoFAHe8v/real-serial-ports

Thank you,

                Mike

[Mike Katz]

Clem,

attach ttix0 line=0,connect=ser0 works but
attach ttox0 line=0,connect=ser0 does not work.

Can I do M6850 style output on TTIX0.  I thought TTIX was input and TTOX was output.

If I can do output, then is it addresses 40 (input) and 41 (output)?

If not, is this a bug in SIMH?

My usb converter works at 110, I've run the teletype on the console.  And for reading and writing binary tapes I believe the teletype is 8E2 for both input and output.  The keyboard on the teletype is 7M2 I believe.  I 'm pretty sure that parity is an option not the standard.

Thank you,

           Mike

On 8/2/2025 7:22 PM, Clem Cole wrote:

BTW: try: attach ttix line=0,Connect=ser0.

And see if that works any better

Note, I'f try this for you but I'm traveling, but I'll try adding a USB port and try running the PDP-8 simulator when I get back to verify the syntax.

I know what it is the document works for the PDP-11 simulator.

On Sat, Aug 2, 2025 at 5:15 PM Clem Cole <cl...@ccc.com> wrote:

This may be helpful.  I have not tried it will the PDP-8 simulator but it should work fine there also, since the coms code in openSIMH is common.  The one thing to watch out for, an ASR 33's default set up is 7 vuitds plus Even parity with 2 bits stops bits at 10 CPS.  That is 110 baud 7E2 

Note aa I point out,not all of the USB chips can support this, so check which one on you have.

Feel free to send me more questions off list.

Clem

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[Steve Tockey]

Mike,

My understanding is that SIMH on the -8 does not really treat the input side different than the output side on serial communication. Everything you do about TTI is mirrored on TTO. You never actually refer to TTO separately, TTI is treated as both input and output. So just set TTI as you want it, and the TTO side should be automatically set the same way.

Hope this helps,

-- steve

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[timr...@gmail.com]

This is what I too was thinking. But was not sure.  Good to know.