mode bit
A flag, usually in hardware, that selects between two (usually quite different)
modes of operation. The connotations are different from flag bit in that mode
bits are mainly written during a boot or set-up phase, are seldom explicitly
read, and seldom change over the lifetime of an ordinary program. The classic
example was the EBCDIC-vs.-ASCII bit (#12) of the Program Status Word of the IBM
360. Another was the bit on a PDP-12 that controlled whether it ran the PDP-8 or
the LINC instruction set.
[Jargon File]
Nearby terms:
MODCAL « Mode « mode « mode bit » MODEF »
MODEL » model
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