For about 11 years I worked as an analogue RF design engineer at a company. In the later years some of the analog circuitry moved into the digital domain with help of DSP’s and/or FPGA’s. I found FPGAs more interesting and I wanted to learn the VHDL language to be able to do RF DSP technics in FPGAs.
At a certain point when I feel more comfortable with the VHDL language, I wrote a simple CPU core and it works! From that moment I getting more and more interested in how CPU internaly works. I searched the web for the early CPUs/computers because I expected that they are simpler and better to understand then the latest CPUs on the marked.
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If you designed your own CPU than probably you are interested about target less compilers. If so, then take look at the end of my links page. |
I was impressed on how to operate an old computer with all those lamps, switches, papertapes, etc….
Then a question came, shall I make a CPU with TTL chips like the PDP-11/44? There is a big disadvantage: more and more TTLs chips getting obsolete.
Then the next question came, shall I make a CPU with through hole discrete components like the pdp-8? I think discrete components will not completely disappear. Maybe through hole, but than we can move to SMT.
I looked at some pdp-8 "straight-8" pictures on for example this site:
That’s a little bit too much I thought. But despite the pictures I started to make some dead bug DTL’s to "play" with it. Very funny, with very few different components I can make all sorts of digital circuits. That will reduce costs because I have to buy a lot of the same components.
Then a colleague notest me on a cheap PCB fusion service which uses standard PCB board sizes to keep prices low. Lets see on how much transistor inverter circuits fits on 5x5cm with a 2.54mm pitch. Eight, a nich number! Even more nicer, all connections are on one site and one hole left!
Then the idee was born, put a 2.54mm pitch trough hole ring on the board edge. Then I can stack four boards with a 90°C twist, which can be laced together with solid copper wire. This is a nice compact construction and cuts connector cost.
Now it seems feasible to build a computer from it with not to high costs.
We shall see ……
