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Tuesday, April 6, 2021

TRACKING WITH CLOSEUPS: Vacuum Tube Computer — Adding Skip to the Instruction Register

The skip logic simply forces an instruction of all ones into the instruction register when the SKIP signal is asserted. This is done with four OR gates with cathode follower buffered outputs to drive the instruction register flip flops. The OR gates are built from semiconductor diodes, which is fair enough since “diode OR” has been used in electronic computer logic circuitry from the very beginning: ENIAC used 7200 “crystal diodes” (or “crystal rectifiers”) as they were called at the time.

Posted at April 6, 2021 13:38