RH11 MASSBUS controller
The RH11 contains 4 registers, plus a share of a fifth; they are
- RHCS1 - Control and Status 1 (shared)
- RHWC - Word Count
- RHBA - Bus Address
- RHCS2 - Control and Status 2
- RHDB - Data Buffer (for maintenance)
As is standard for the MASSBUS, all the other device registers are in the device.
Two of them hex-sized:
- M7294 - DBC - Data Buffer and Control
- M7295 - BCT - Bus Control
Two dual-sized cards containing controller logic:
- M7296 - CSR - Control and Status
- M7297 - PAC - Parity Generation and Checking
Three dual-height M5904 MASSBUS transceiver modules.
Optionally one or two (see below) single-height cards:
- M688 - UNIBUS Power Fail Driver
The RH11 backplane also contained three SPC slots in otherwise-unused slots.
The RH11 contains connectors and circuitry for two separate UNIBUSes; the second UNIBUS is primarily used on systems with multi-port memory, such as the PDP-11/45. If no CPU is connected to UNIBUS B, an M9300 terminator at the start of the bus can be configured to do NPR grants. A jumper allows the RH11 to do block transfers on UNIBUS B without going through an arbitration cycle.