View Full Version : A new PDP-11 S100 bus CPU board.

May 5th, 2017, 05:21 PM
After 5 months in the making, I am delighted to report another new S100 board to our collection of S100 boards. This board is called the PDP-11 CPU S100 board. It incorporates the Digital PDP-J11 chip. The PDP-11 architecture is an instruction set architecture developed by Digital Equipment Corporation (DEC) during the early 1970's. It was implemented by LSI central processing units (CPUs) and microprocessors used in PDP-11 minicomputers. It was in wide use for most of the 1970s. It is a 16 bit CPU with up to 4MB of RAM addressing capability.

I use the approach I have in the past of using a CPLD to translate the PDP signals into S100 signals. This was my first exposure to programming the PDP-11 chip. I wrote as simple ROM based monitor for the board. I now see why the PDP-11 was so popular with programmers. Itís a real joy to program. Was way ahead of its time! Users can write their own assembly code and play with it.* The thing is fast too; currently I have it running with an S100 bus Phi clock of 12MHz.
Please see here for more information.

I anticipate a large demand for this board. Experience has thought me that keeping track of board orders is quite a time consuming task. If you would like one or more of these bare boards add your name here:

Do NOT e-mail me directly. The board is $18/board + shipping. Payment is with PayPal upon receipt of the board. I will leave the order open for only 1 week Every day or two I will update the order names on this page.


Check your name appears here a few days later. Only orders on this page will go out. The boards will be done (two layer boards) by PCBCart (China). Should take 3-4 weeks. If you have not ordered a board before I will contact you later for a shipping address.

Paul Birkel is also putting together a bulk order for the KDJ11 chip. Search this forum for more info. Paul can you update details.

I want to point out two things. First this is not a simple S100 board and is definitely not for beginners. The components are expensive (the J11 chip costs ~$60-$100 alone). The GALs and CPLD need to be programmed and for most, extensive reading about Digital Setups (hardware and Software) will be required.

Second, I have started on a PDP-11 Support board. Currently I see no reason why eventually we cannot get a Digital DL11-W + TU58 emulator on an S100 board so one could run an OS like RT11. However there are many variables and a few unknowns, it is possible this CPU board will need to be replaced by a later version.

Please read carefully the above web page before jumping into what is a long process. Fun, but a large undertaking.

John Monahan

May 6th, 2017, 08:58 AM
Awesome, added my name to the list! I've got an Alpha Micro board that uses the WD16 chipset (LSI-11).

Thanks for making this available to the community!

May 6th, 2017, 09:17 AM
Hi All;

John, I think I sent a message for an order for one Board..

Glitch, I sent You a private message..


May 6th, 2017, 02:37 PM
I've got an Alpha Micro board that uses the WD16 chipset (LSI-11).

Is the WD16 pin compatible with the J11?

May 6th, 2017, 06:51 PM
Is the WD16 pin compatible with the J11?

Short answer: NO

The LSI-11 chipset was the first LSI PDP-11 implementation from DEC. The J11 chip was the last.

The LSI-11 chipset consists of multiple 40-pin DIP parts. A Control Chip and a Data Chip (designed by Western Digital), and one or more MICROM (512 x 22 bit microcode ROM). A standard LSI-11 board will have two MICROM chips to implement the base PDP-11 instruction set and a third socket for an optional EIS/FIS instruction set MICROM. There were some other CPU implementations that used the Control Chip and the Data Chip with custom MICROM chips.

For example the Western Digital WD9000 Pascal Microengine:

The J11 is a single hybrid 60-pin DIP part with the Control Chip and the Control Chip mounted on it. There is no writeable control store option for the J11.

DCJ11 Microprocessor User's Guide: