QBUS

The QBUS, previously known as the "LSI-11 bus", was intended as a cheaper alternative to the UNIBUS system by Digital Equipment Corporation.

It was widely used in PDP-11s and VAXen.

The bus had multiplexed address and data lines, and was available in 16-, 18-, and 22-bit configurations.

Important note: The 16-bit and 18/22-bit backplanes are electrically incompatible and mixing the two may damage cards on the bus.

Signalling

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Pinout

QBUS pins are identified in the standard UNIBUS manner; there are two connectors, A and B; pins on the component side are 1, those on the solder side are 2. Pins are identified by the 'DEC alphabet', A-V, with G, I, O and Q dropped.

By signal

 Ground	AJ1
 Ground	AM1
 Ground	AT1
 Ground	AC2
 Ground	BJ1
 Ground	BM1
 Ground	BT1
 Ground	BC2
 +5		AA2
 +5		BV1
 +5		BA2
 +5B		AE1 *
 +5B		AS1 *
 +5B		AV1
 +12		AD2
 +12		BD2
 +12B		AS1 *
 +12B		BS1
 -12		AB2
 -12		BB2

 BDAL00	AU2
 BDAL01	AV2
 BDAL02	BE2
 BDAL03	BF2
 BDAL04	BH2
 BDAL05	BJ2
 BDAL06	BK2
 BDAL07	BL2
 BDAL08	BM2
 BDAL09	BN2
 BDAL10	BP2
 BDAL11	BR2
 BDAL12	BS2
 BDAL13	BT2
 BDAL14	BU2
 BDAL15	BV2
 BDAL16	AC1
 BDAL17	AD1
 BDAL18	BC1
 BDAL19	BD1
 BDAL20	BE1
 BDAL21	BF1

 BBS7		AP2
 BDIN		AH2
 BDOUT		AE2
 BREF		AR1
 BRPLY		AF2
 BSACK		BN1
 BSYNC		AJ2
 BWTBT		AK2

 BDCOK		BA1
 BEVNT		BR1
 BHALT		AP1
 BINIT		AT2
 BPOK		BB1

 BDMGI		AR2
 BDMGO		AS2
 BDMR		AN1
 BIAKI		AM2
 BIAKO		AN2
 BIRQ4		AL2
 BIRQ5		AA1
 BIRQ6		AB1
 BIRQ7		BP1

 SRUN		AH1 *

 ASpare2	BU1
 MSpareA	AK1
 MSpareB	AL1
 MSpareB	BK1
 MSpareB	BL1
 PSpare1	AU1
 PSpare2	BU1
 PSpare4	BS1
 SSpare1	AE1 *
 SSpare2	AF1
 SSpare3	AH1 *
 SSpare8	BH1

Signals marked with a "*" show cases where two signals use the same pin (not at the same time, obviously).