RH11 MASSBUS controller
The registers in the RH11 are only accesssible from the 'first' UNIBUS (UNIBUS 'A'); likewise, interrupts of the CPU are only possible via UNIBUS 'A'. The RH11 can be set under software control to do DMA data transfers on either the first or second UNIBUS (UNIBUS 'B').
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; the 'A' UNIBUS has a mode where it does two DMA cycles per grant.
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.