Search Posts:

PDP 11/40 M7656 Serial Comms


Return to Threads

  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



Buy a Commodore Computer Poster

Popular Topics and FAQs

  • Commodore B Series Tips and Tricks
  • Aerocomp TRS 80 M 1 Expansion Unit DDC
  • Items Wanted
  • Lobo Max 80
  • Zenith Z-19-CN
  • Prototype PET 2001 photo
  • Using Toggle Switches to Analyze Memory
  • Commodore Disk Archive Project
  • PET 2001 Prototype at Gametronics 1977
  • Jim Butterfield Photo
  • IMSAI 8080 With Processor Tech. Cutter
  • Secrecy is the keystone of all tyranny
  • Cromemco System Three
  • Northstar Horizon - Boot Problem
  • Computer History and Restoration Links
  • Commodore BX-256-80 - 8088 Co-processor
  • S-100 board testing with Z-80 ICE
  • Donner 3500 - an early portable computer
  • Digital (DEC) PDP 11/05 NC Assembly
  • Univac 1219 rescue
  • Fido BBS listing node list 6-13-1986
  • PDP 8e
  • MITS 88-2 SIO (2SIO) for BASIC
  • Visual Technology Inc Model 1050
  • Amiga 2500 Restoration
  • The Evolution Of IBM Computers
  • Replacement teletype print hammer head
  • Archiving and Copying Software 101
  • Computers Built 1940 - 1950
  • CBM B-520 (a.k.a B256-80 or B500 256)
  • RCA COSMAC Microkit
  • Commodore 64K C-116 Mods
  • MITS 8800b Turnmon 9600 baud
  • Catweasel, 8in and 5 1/4
  • Raspberry Pi as Gateway to Internet
  • Digital PDP11 late 1969 early 1970
  • PDP 11/40 72 inch cabinet model
  • PDP 11/40 Industrial 11 model
  • Digitial MicroVAX 3100 30 System
  • Digital VAX 4000-200
  • Commodore 64 / 1541 DRIVEKNOCK
  • Booting the System Using RL02 drive
  • PACS: Reflections by Kathleen Mauchly
  • Tele-Graphic Computer Systems Inc.
  • Commodore B Series SID Jukebox?
  • Installing Core into PDP 11/40
  • Setting Up OpenVMS 7.1 DNS CLERK
  • Felt-Tarrant Comptometer Model J
  • NextStation Color
  • Digital Rainbow (PC100-B2)
  • 1970 Compusad Compulogical Tutor
  • Archiving Papertapes Using DSI NC 2400
  • 1976 P.C.C. Features the MAI JOLT 6502
  • 1961 Beckman DEXTIR Computer
  • UNIVAC 1 and UNIVAC File Computer 1
  • Past Issues:

    BRYANS Analog Plotter

    This image was selected at random from the archive. Click image for more photos and files from this set.