M9302 UNIBUS terminator

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M9302 terminator card

The M9302 UNIBUS terminator is a terminator for the UNIBUS; it provides all three functions of a UNIBUS terminator. The M9302 is a dual format card, intended for use in the two top (AB) sections of a MUD slot, or in a UNIBUS in/out slot.

It is a replacement for the original M930 UNIBUS terminator, with so-called 'SACK Turnaround' functionality added.

Note that as a result of the 'SACK Turnaround' circuitry, if there's any break in a bus grant line (perhaps a missing grant continuity card) at any point before it gets to the M9302, the M9302 will jam SACK on. That is because the resulting 'open' input to the TTL gate monitoring the grant line in the device immediately down-stream from the break (perhaps in the M9302) will float high, thereby looking like a permanent incoming grant, which will be turned around by the M9302 as a permanent assertion of SACK. (In many PDP-11 CPUs, that will freeze the CPU.)

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