FPGA VAX update, now DIY TTL computers

Stegeman, Henk HJ SITI-ITIBHW5 henk.stegeman at shell.com
Tue Nov 8 03:41:58 CST 2005

Hi Jos, 
I fully agree with you. Building your own CPU is really an exciting project. 
I took me more then 3 months to debug my 110 TTL CPU with 
256 words of micro code of 48 bits.   
See: http://www.anysystems.nl/hjs22.html  for some pictures and the 
reference card.
I build this CPU & IO unit in 1976. A liitle bit younger then the 
Elektor machine :-).    Do you still have the Elektor machine ?
Regards Henk Stegeman.
> What surprises me about the home-built computers from scratch is the 
> lack
> of imagination when it comes to architecture.  Most are basically
> one-address-cum-accumulator designs.  It would seem that larger 
> register
> files are much easier to build nowadays and would open up the door to 
> some
> 2 and 3-address designs.
The reason is the effort it takes......
Ask anybody who actually  made a CPU  ( I myself did a 12 bit
  TTL based, single address single accumulator machine).
The real effort is actually building and debugging the unit.
  There is only so much time you have....
> I've always thought that 24 bits is a nice word size for a small 
> computer.
Much too big to actually build in TTL.
In 1974 Elektor magazine started a series of DIY articles that described
an extensible ( 12 bit or 16 bit width ) three address, clockless 
TTL based, with a shiftregister based memory.  (6 or 8 512x2 
shiftregisters .)
An expensive extra wasa 2102 based RAM.
The machine did hardware multiply and divide +
Instructions were build into the address map .i,e, address  XX is the 
adder, adress yy is a shift and so on..
The start of this series actually predates the Mark8  computer !
                                                                            Jos Dreesen

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