RH11 MASSBUS controller
The RH11 consisted of a double system unit into which plugged a number of cards, two of them hex-sized, a 'Bus Control' module, and a 'Data Buffer and Control' module. (The RH11 backplane also contained three [[SPC}] slots.)
As is standard for the MASSBUS, all the device registers are in the device; the RH11 merely allows the MASSBUS and UNIBUS to communicate.
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.
The RH11 has the capability to operate in 18-bit mode; in this mode, the PA and PB UNIBUS lines are used for data bits 16 and 17.