Ken tinkers with DTL, and SV3ORA’s transistorized 4-bit digital computer made out of discrete DTL

July 9, 2014 | Homebrew CPU, Homebuilt CPUs | By: Mark VandeWettering

Ken stumbled on one of my earlier posts about DTL (diode transistor logic) and was interested enough to do some basic exploration. He reduced the DTL NAND gate to a double diode, a transistor and two resistors. Ken sent me the LTSpice and EagleCAD screen dumps that fit in about .4″ square:


Pretty cool. In an email, Ken goes a bit further:

I’m working towards a bitslice pcb that implements either an ALU or a Program counter. Remarkably their logic is so similar that a single block of logic could be configured to match either requirement. I think I can get it all on to a 4″ x 2″ pcb with a couple of LEDs and a toggle switch on the front edge. Stack 8, 12 or 16 of these together and you have something similar to the PDP-8.

Awesome Ken! I hope to hear more about this when you have some hardware running.

I haven’t even done any real thinking since then, but I went back and tried to find some more information of people building stuff with DTL logic. I’m not sure if I spotted SV3ORA’s 4 bit digital computer before, but rereading it today, it turned out very cool. He constructed the logic on perfboard with just ordinary components. Very nice.

A transistorized 4-bit digital computer made out of discrete DTL

Addendum: Ken also pointed out the NAND to Tetris course in his email, which I believe I may have blogged about before, but which is a great resource for someone seeking to develop a more complete vertical understanding of computers from the ground up. Ken’s addition of actual soldering to the project makes it even cooler.

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Comment from kiwimonster
Time 7/10/2014 at 1:57 pm

I’m reminded of the 4-bit computer I designed and put together as a college project made out of TTL components. in 1988. It was put together in a collection of solderless breadboards so it was a mass of wires that looked like a mess, but it (eventually) worked.

This effort looks cooler.

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