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-address-bit configurations (data width remained 16 bits in all three versions).
Important note: The 16-bit and 18/22-bit backplanes are electrically incompatible and mixing the two may damage cards on the bus.
It is possible to upgrade 18-bit backplanes to 22-bit; see Upgrading QBUS backplanes.
Signalling
Like the UNIBUS, there are three basic kinds of cycles on the QBUS: data read/write cycles (in which a 'master' reads or writes data to/from a 'slave', which is usually, but not always, memory); DMA cycles (in which a device gains control of the bus so that it can do a read/write cycle); and interrupt cycles, in which a device causes the CPU to perform an interrupt.
All QBUS transactions are asynchronous, and use interlocked request/response signals for control and timing.
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
| Signal | Pin |
|---|---|
| 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).
By pin
| Signal | Pin |
|---|---|
| BIRQ5 | AA1 (old BSpare1) |
| BIRQ6 | AB1 (old BSpare2) |
| BDAL16 | AC1 (old BSpare3) |
| BDAL17 | AD1 (old BSpare4) |
| SSpare1 | AE1 (alt +5B) |
| SSpare2 | AF1 (alt SRUN/SMENBL on CF1) |
| SSpare3 | AH1 (alt SRUN on CH1) |
| Ground | AJ1 |
| MSpareA | AK1 |
| MSpareB | AL1 |
| Ground | AM1 |
| BDMR | AN1 |
| BHALT | AP1 |
| BREF | AR1 |
| +5B/+12B | AS1 (old PSpare3) |
| Ground | AT1 |
| PSpare1 | AU1 |
| +5B | AV1 |
| +5 | AA2 |
| -12/-5 | AB2 |
| Ground | AC2 |
| +12 | AD2 |
| BDOUT | AE2 |
| BRPLY | AF2 |
| BDIN | AH2 |
| BSYNC | AJ2 |
| BWTBT | AK2 |
| BIRQ4 | AL2 (was BIRQ) |
| BIAKI | AM2 |
| BIAKO | AN2 |
| BBS7 | AP2 |
| BDMGI | AR2 |
| BDMGO | AS2 |
| BINIT | AT2 |
| BDAL00 | AU2 |
| BDAL01 | AV2 |
| BDCOK | BA1 |
| BPOK | BB1 |
| BDAL18 | BC1 (old SSpare4) |
| BDAL19 | BD1 (old SSpare5) |
| BDAL20 | BE1 (old SSpare6) |
| BDAL21 | BF1 (old SSpare7) |
| SSpare8 | BH1 |
| Ground | BJ1 |
| MSpareB | BK1 |
| MSpareB | BL1 |
| Ground | BM1 |
| BSACK | BN1 |
| BIRQ7 | BP1 (old PSpare6) |
| BEVNT | BR1 |
| PSpare4/+12B | BS1 |
| Ground | BT1 |
| PSpare2 | BU1 |
| +5 | BV1 |
| +5 | BA2 |
| -12/-5 | BB2 |
| Ground | BC2 |
| +12 | BD2 |
| 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
See also |
