DB11-A Bus Repeater

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The DB11-A Bus Repeater allows a UNIBUS to double the number of peripherals connected to the bus (in terms of the combined analog load).

It terminates (in analog terms) the first section of the bus, and active digital logic repeats all the signals though onto the second section (or from the second back to the first, when required); the two sections are thus logically connected, but not in purely analog terms.

It consists of a custom system unit backplane, holding a number of smaller FLIP CHIPs; mostly singles (see table below), with one dual (M7213).

Type Count Function
M783 1 Bus driver
M784 1 Bus receiver
M785 4 Bus transceiver
M7212 3 Address buffer
M7213 1 Buffer master
M7248 1 BBSY repeater
M930 2 UNIBUS terminator

Board locations (as seen from the board insertion side of the backplane, not the wire-wrap pin side, as is common in DEC documentation) are:

Slot A B C D E F
1 UNIBUS A In M7248 M7212 M7212 M7212
2 UNIBUS A termination Unused M784 M783
3 Power Unused M7213 M785 M785
4 UNIBUS B Out UNIBUS B termination M785 M785

For installation in later BA11 mounting boxes, the paddle card of a G772 system unit harness adaptor can be plugged into the 3A slot; the DEC power distribution connectors on the other end of the adaptor plug into those of the BA11.

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