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PDP 11/40 M7656 Serial Comms


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  PDP 11/40 M7656 Serial Comms by Bill Degnan - 03/16/2015 08:17
Now that the core system is running again I can turn my attention to adding a display and disk drives to the system.

I have a M7856 10 F-C (RS232 WITH 19.2 OPTION?) i.e. serial card and few terminals including a vt52 a LA36

Instructions for booting the PDP 11/40 using RL02 drives

Next - I will replace one of the grant continuity cards and put in a M7762 (RL02 controller) in its place and attempt to boot from RL02 using M9312 ROM boot terminator card with RL02 ROM chip installed.

I had a hopefully still working RL02 (01) and I bought a second drive from Ian last year (02). I have 10 or so RL02 packs, at least one should be a RT11 boot disk.

  M7856 Setup by Bill Degnan - 03/18/2015 10:48
M7856 BERG Connector
Using guidance found in documentation and web resources I found the correct pin assignments for a serial console cable to connect from the M7856 to a serial terminal. Fortunately I had a BERG connector available. I set the jumpers to 9600 baud. Click image for larger view.

Null Modem adapter
Next I attached the EIN cable end to a null modem adapter and a longer straight-through cable. The end of the straight-through cable was attached to the COMM port of a VT 102 terminal set to 9600 baud.

PDP 11/40 with VT-102 terminal
This photo shows the PDP 11/40 with VT-102.

PDP 11 echo character program output
I toggled in a program that takes characters typed at the terminal, passes them through the PDP 11/40 and echoes them back to the terminal screen.

The progress thus far was short-lived. The system returned to an AC LO failure condition ((see thread))and the 5 amp fuse blew out. I have parts on order so I can make more permanent repairs. But at least I got a little taste of the machine. I should have waited until I finished the power supply repairs but I was impatient, can you blame me?

The RAM board was kind of flakey, I need to replace the caps on this card as well as the power supply control board's caps and resistors that have failed.

  Downloading programs via serial card by Bill Degnan - 07/18/2015 14:18
Power supply appears to be fixed after repairs and running for a few hours. We're now back to the point of being able to use a terminal to echo characters.

Next, we need to toggle in a bootstrap loader and download the absolute loader into memory. From there we can load BASIC or other programs.

Bootstraps Here



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