Suppose one wanted simulate one in modern components.
How would you
do it, if you had, say, a million bits to store?
Fewest parts would be to use a FIFO feeding the "O" back to the "I"
I had thought about building a state sequencer this way once for a project
where the sequence was of programmable length, but didn't require branching.
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The ADM3 'A' version differed from the original by replacing the recirculating
shift registers with 2102's and a 10 bit counter.