• Optimized ALU for computers with 4PDT relays

    09/26/2019 at 03:49 • 7 comments

    Taking inspiration from Roelh's "Simple Relay ALU" and from JHallen's one found in the "Single Board Relay Computer" I designed a version that is providing 10 functions (1 addition, 6 bitwise logics, 1 shifter and 2 trivial ones) with the same 16 relays for 8bit as in Konrad Zuse's one, and keeping the fast carry feature. And with just 12 relays it is possible to have ADD, AND, OR and even SHR (shift right), and SHL using the addition, for me the sweet spot to be used. The NOT (useful also for the subtractions) in my case is coming from the A registry relays.

    The diagrams below show the connections of the bit slice with full adder and logic outputs, and the functionalities available. 

    The fixed numbers 0 and 1 are coming from the instruction.decoding, while a multiplexer 4:1 (done with 6 4PDTs) selects for F0 among instruction values, A, not A, or An+1 (for the shift right). A 2:1 multiplexer (done with 2 4PDTs) is added at the end to select among ADD or bitwise logic function result