Difference between revisions of "M9302 UNIBUS terminator"
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It is a replacement for the original [[M930 UNIBUS terminator]], with so-called 'SACK Turnaround' functionality added. | 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]] | + | 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 (hanging the machine so that it will not run at all; this is fairly easy to recognize and fix). That is because the resulting 'open' input to the [[transistor-transistor logic|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. (As mentioned, in many [[PDP-11]] [[Central Processing Unit|CPUs]], that will [[KY11-L to CPU interface|freeze the CPU]].) |
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| + | ==See also== | ||
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| + | * [[M8264 No-SACK Timeout Module]] | ||
==External links== | ==External links== | ||
Latest revision as of 13:35, 25 August 2024
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 (hanging the machine so that it will not run at all; this is fairly easy to recognize and fix). 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. (As mentioned, in many PDP-11 CPUs, that will freeze the CPU.)
See also
External links
- 11/34 Vol. 2 Field Maintenance Print Set - the M9302 is covered on pp. 68-69 of the PDF
