Unibus

Unibus was one of many bus technologies used with PDP-11 and early VAX systems manufactured by Digital Equipment Corporation Maynard, Massachusetts.

Unibus cables were composed of 72 wires (2 connectors x 36 lines). When not counting the power and ground lines, it is usually referred to as a 56 line bus.

18 A00-A17 - Address Lines
16 D00-D15 - Data Lines
 4 BR4-BR7 - bus requests
 4 BG4-BG7 - bus grants
 1 ACLO    - AC Low
 1 DCLO    - DC Low
 1 MSYNC   - Master Sync
 1 SSYNC   - Slave Sync
 1 NPR     - Non Processor Request (DMA)
 1 NPG     - Non Proccessor Grant  (DMA)
 1 BBSY    - Bus Busy
 1 SACK    - Selection Acknowledge
 1 INIT    - Bus Init
 1 INTR    - Interrupt Request
 2 PA-PB   - Parity Data from Memory Controllers
 2 C0-C1   - Control Lines
 2 +5v     - Power Lines (not counted as part of the 56)
14 Gnd     - Ground Lines (not counted as part of the 56)