Schematics of Atanasoff-Berry Computer logic circuits?

Brent Hilpert hilpert at
Thu Aug 21 17:25:39 CDT 2008

DI Gerhard Kreuzer wrote:
>    The schematic is quite simple, maybe you can remember the first
> logic chips available where made in so called RTL (restistor
> Transistor logic), which is exactly the same as the ASM do, only the
> levels are shifted.
>    Because of the problems with the resistor networks, the so called
> TTL chips are developed, which replaces some resistors by transistors.
>    I am shure there is enough information out. Once you have seen how
> RTL works, you will easily find out how ASM works.

(As much as I like to call the ASM logic "RVL" (Resistor-Vacuum-Logic)),
the (gate input) design of the ASM logic is not the same as that of RTL.
It is not simply a swap of transistors for vacuum tubes, they are
fundamentally different approaches to gate design, at least if we're
talking about the common families of RTL ICs (that I've seen internal
schematics for).

The ASM gates have a purely resistive summing point of the input resistors
and a bias resistor before feeding into a single non-linear device (tube grid).
Further it achieves different gate types by simple varying the (bias) resistor

In RTL the summing point is multiple transistor collectors with a common load
resistor: each input has it's own saturating non-linear device to
"discretize" levels before feeding into the summing point.
(And only one gate type is targetted)

Consequently, the ASM circuit is far more finicky and tight in it's requirements.

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