In article , Clive D. W. Feather
writes
Actually, I think you'll find that numbers on programme machine
controlled lines only went up to 377 - there were 8 bits for train
number.

The PM data I've seen wasn't organised by 8-bit byte, but simply had a
number of bits for each field. I thought that there were 6 minute bits,
5 hour bits, and a half-minute bit, but I could be misremembering here.

Reading through an IRSE booklet, it shows 8 bits for train number (hence
000 to 377). Some machines had a 5 bit "time to next event" field,
giving times from 0.5 to 15.5 minutes. Others had an 11 bit time field
(4 hour, 6 minute, plus half-minute). The timer device recorded time in
the form day (0 to 15), am/pm, hour (4 bits), minutes (6 bits), and
half-minute, with the last 11 bits being compared against the 11 bits on
the punched roll.

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