Ingolf's first                         
       Personal Computers       

In the late 60's the Physics Institute of the Hamburg University, where I was working on my thesis, acquired a Digital Equipment PDP 8E minicomputer.  This computer was meant for process control and calculation, however the main application was a game "lunar landing".  Some people were really addicted and "worked" long hours.  Familiar with digital circuits I wanted to build my own computer.  The PDP 8E was still using core memory and boards full with low integration TTL circuits.  Intel had not yet introduced the first microcomputers (4004 and 8008), the first DRAM 1103 and EPROMs 1702. 
I decided to build a serial version of the PDP 8 with MOS shift registers as memory.   

Front view of my computer IR 3

There are 12 red buttons to set the bits of a word which can be stored into the memory.  A row of 12 incandescent lights (see picture to the right) displays the content of the accumulator or the memory cells.  A row of 8 lights displays the memory address.  A switch selects the modes: load "L", display "P",  run "R", single step "ES".

The computer - unfolded

The diagram to the left shows the architecture of my computer.  There are 2 shift registers - 768 bit long - which store a total of 128  12bit words.   An additional 32 word ROM (read only memory) is programmed with fixed routines.  In the shift registers the information circulates, a selected word (sequence of 12 bits) can be overwritten with new data.

A timing generator generates bit clock pulses (1 MHz), word clock pulses and the major states FETCH and EXECUTE.  During the FETCH phase the memory address is taken from the program counter and during the EXECUTE phase it is taken from the instruction register. 

The instruction set is similar to the set of the PDP 8E.  
TAD   (two's complement addition memory to accumulator)
AND   (logical AND of memory and accumulator)
DCA   (deposit and clear accumulator)
JUMP (jump to memory address)
In addition there are SKIP instructions for conditional branching and Input/Output instructions. 
Subroutines are handled by DPC (Deposit Program Counter) and MPC (Memory to Program Counter - a kind of indirect jump).

In the arithmetic unit the operations addition and   logical AND are performed.  In a serial machine the circuits for these operations are very simple, only 1 bit at the time is processed. 
Input / Output  interact with external devices.

3 MOS shift registers FDN 196
with their clock drivers

My ROM memory:  Up to 32 words of 12 bit data are stored in rows of semiconductor diodes.  4 IC's contain addressing cuicuits

My computer IR3 became operational in 1972.  It ran little programs, it played simple music, and it did some useful work by collecting data and storing the data to a magnetic tape recorder. 



Later I built more advanced computers, with a Zilog Z 80 microcomputer, 4K RAM, and 4K ROM.   A minicassette served as external data storage device.  For software I wrote a Tiny Basic interpreter, and an assembler program. 

My computer IR6, completed in 1981


A printed circuit board with Z 80 microcomputer


Some Applications

mozart.jpg (73431 bytes)       mao.jpg (65550 bytes)
I was very proud of a music program which played Mozart's   "Ein Musikalisches Wuerfelspiel"   (musical dice).
Modern Version  
Maybe, my computer IR6 was the first personal computer worldwide connected to a rewritable optical disk. ( A project, which I was working on at the Philips Research Lab in Hamburg/Germany)
Ingolf's Projects
Ingolf's Professional Career Ingolf's Parallel Career
Ingolf's First Personal Computers to measure is to know
Hand - Eye Coordination RoboGames
Model of a Windmill Jumping Jack
Dollhouse Ingolf's Big Picture
Sonogram Viewport
Line follower  

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