Given the goal to keep costs low, compromises had to be made on how peripherals are treated.

 

See the second half of the Youtube movie for a demonstration: USB sticks are used as if they are paper tapes. Hard disks are replaced by SD cards. But the operational steps to load them are kept the same, and the original software is used at all times.

... behind the blinking lights

 

... sits a Raspberry Pi, running a modified version of SimH. Of course, some will prefer more or less authentic PDP-8 components such as the Intersil 6120, or use an FPGA. But those directions would explode costs, given all the I/O connectors you need to emulate the PDP-8 peripherals (how about adding a few extra terminals?). More importantly, it would be unlikely to achieve the same compatibility and feature list that SimH offers.

Compatible with the Raspberry

Pi 4, 3, 2, B+, A+, Zero W & Zero

Back of the (prototype) panel, with a Raspberry Pi Model A+ installed

Flexibility

 

Basically, the PiDP-8 is a PDP-8/I front panel for a Raspberry Pi. You can still use the Pi plugged in to it for any other purposes. But the Pi/SimH combination offers an incredible flexibility for a PDP environment:

 

  • Connect multiple terminals through SSH, Telnet, Ethernet, WiFi or the serial port. Or hook up a HDMI monitor and PS/2 keyboard. Without the PDP-8 knowing the difference.
     

  • Use the Pi's SD card to store a complete library of paper/DECtapes, floppy/hard disks.
    Or use USB sticks as removable storage - one stick contains your FOCAL69 paper tape, another an OS/8 disk cartridge.

     

  • Operate the PDP-8 as you should, through the front panel. Or cheat by stepping out into SimH's debugging environment for a moment, to quickly disassemble code or whatever.

Beauty and the beholder's eye

 

Are PDP-8s beautiful? Works of art even? Depends on your attitude towards 1970's color schemes.

 

But it sure was iconic.

 

The PiDP is intended to celebrate the PDP-8's 50th birthday, and hopefully it's pretty enough to find a place in the living room. Because it can be accessed over WiFi, it does not need any cables to hook it up. In fact, put a LiPo battery in the case and it could run for up to 30 hours without any wires at all.

PiDP-8/I: RECREATING THE PDP-8/I

CELEBRATING 50 YEARS OF PROGRAMMED DATA PROCESSING

Overview

 

Project goal: to create a faithful but low-cost replica of the 1968 PDP-8/I. Operated through the Blinkenlights front panel, it should evoke the user experience from the past. It should also replicate all stages in the PDP-8's development. Which is not trivial, because the PDP-8 series spanned a long period in computer history: from 1965 to 1979 and from teletype & paper tape all the way through to hard disks and multi-user systems.

 

Proper Credit Where It's Due

 

It should be clear from the above that the PiDP is a rather simple piece of hardware that owes its features to SimH, the emulation project from Bob Supnik and hs many collaborators. All I did was to add code to drive the physical front panel, and probably introduce a few bugs into what was a flawless emulator. Sorry for that, and thank you for sharing the code!

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