Barry J. Stern's PDP-8 Page

Indianapolis, Indiana

Email: bjstern2@comcast.net

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Project: PDP-8 Computer

Introduction

The PDP8 is the Model T of the Personal Computer Revolution. Starting at 4K with a Teletype paper tape system, the PDP8 family was expandable to 32K with floppy drives and an OS8 operating system, giving the system the capability of a CP/M System. Designed before the advent of Integrated Circuits and inexpensive registers for Stack Pointers and Index Registers, the Instruction Set of the PDP8 is remarkably efficient. The popularity of the system led to the Intersil 6100 as an Integrated Circuit version.

Demonstration of Chess

To demonstrate the operation of the Computer depress Caps Lock on your Keyboard. Load the program Chess into the computer by selecting Chess in the List Box and pressing Load. If Chess loads properly, the PC will contain the octal number 200. Now press Start.
The Computer will print:
CHEKMO-II
W. YOUR MOVE?
Now enter E2-E4 followed by depression of the Enter Key on your keyboard.
The Computer will print:
B. YOUR MOVE?
Now enter PB followed by depression of the Enter Key on your keyboard.
The Computer will print:
B. E7-E5
W. YOUR MOVE?
Note that there is a delay between printing B. and E7-E5 as the computer calculates its move.
Now enter BD followed by depression of the Enter Key on your keyboard.
The Computer will print out the complete Board.
Chess has a complete set of commands and error responses. These may be obtained from David Gesswein's Web site: Chess Index

Demonstration of Focal

To demonstrate the operation of the Computer, load the program Focal into the computer by selecting Focal in the List Box and depressing Load. If Focal loaded properly, the PC will contain the octal number 200. Now press Start.
The computer will print a * on the TTY.
Place a cursor after the * by clicking anywhere on the TTY.
Now enter T followed by a space and then 6+5 followed by Enter.
The computer should response on a new line with = 11.0000*.
A more sophisticated entry would be T followed by a space and then FSQT(2) followed by Enter.
The computer should respond on a new line with = 1.4142*
Clicking on the Clear button will clear the TTY screen.
Depress Clear and then Enter.
The computer should respond with a clear screen and the prompt *.
Now enter GO followed by Enter.
The computer will run the Focal program "Prime Factors of Positive Integers". Focal has a complete set of commands, operations, functions, and error messages. These may be obtained from Doug Jones's Web site: PDP8 Index

Assembly Language Programs

There are three assembly language programs. They are up, factor, and prime. The procedure for loading and running these programs are the same as with Focal. The assembly language listing for the up counter program is as follows.
Location Operation Comment
*0000
START, IAC /INCREMENT ACCUMULATOR
HLT /HALT THE COMPUTER
JMP START /JUMP BACK TO START

To assemble this program one can use the cross assembler written in Java Script by Mark Arnold at Assembler 

UW PDP-8 CROSS ASSEMBLER JavaScript version ST 8/4/96
 
          *0000
0000/7001 START,  IAC       /INCREMENT THE ACCUMULATOR
0001/7402         HLT       /HALT THE COMPUTER
0002/5000         JMP START /JUMP TO START
          /
 
SYMBOL TABLE
 
START   0000

Downloadable Version

For the student who would like to write and save programs a Visual J++ 6.0 version with Doug Jone's pal assembler is contained in the Pdp8.zip file. This program requires that the Microsoft Virtual Machine be installed on your system.