View source for RH11 MASSBUS controller

The '''RH11 MASSBUS controller''' (technically, the '''RH11-AB''') allowed the interconnection of [[MASSBUS]] devices such as the [[RP04 disk drive|RP04]] to systems with a [[UNIBUS]], primarily on [[PDP-11]]'s.

The RH11 has the capability to operate in [[UNIBUS parity#18-bit width|18-bit mode]]; in this mode, the PA and PB UNIBUS [[parity]] lines are used for data bits 16 and 17. The [[KS10]] made use of this capability.

==Second UNIBUS==

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]].

The [[register]]s in the RH11 are only accesssible from the 'first' UNIBUS (UNIBUS 'A'); likewise, [[interrupt]]s of the [[Central Processing Unit|CPU]] are only possible via UNIBUS 'A'. The RH11 can be set under [[software]] control to do [[Direct Memory Access|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 [[Non-Processor Request|NPR]] [[bus grant]]s. 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.

==Registers==

The RH11 contains 4 [[register]]s, 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.

==Hardware==

The RH11 consisted of a double [[system unit]] [[backplane]] (below) into which plugged a number of cards:

Two of them [[DEC card form factor|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 single-height cards:

* M688 - UNIBUS Power Fail Driver

The RH11 backplane also contained three [[Small Peripheral Controller|SPC]] slots in otherwise-unused slots.

===Backplane layout===

Board locations (as seen from the board insertion side of the backplane, not the [[wire-wrap]] pin side, as is common in [[DEC]] documentation) are:

{| class="wikitable"
! !! colspan="6" | Connector
|-
! Slot !! A !! B !! C !! D !! E !! F
|-
| 1 || colspan="2" style="text-align:center;" | UNIBUS A In || colspan="2" style="text-align:center;" | M7297 Parity || colspan="2" style="text-align:center;" | M7296 Control/Status
|-
| 2 || colspan="6" style="text-align:center;" | M7295 Bus Control
|-
| 3 || colspan="6" style="text-align:center;" | M7294 Data/Buffer Control
|-
| 4 || colspan="2" style="text-align:center;" | Unused || colspan="2" style="text-align:center;" | M5904 Transceiver || M688 - UNIBUS B Power Fail || Unused
|-
| 5 || colspan="2" style="text-align:center;" | Unused || colspan="2" style="text-align:center;" | M5904 Transceiver || M688 - UNIBUS A Power Fail || Unused
|-
| 6 || colspan="2" style="text-align:center;" | Unused || colspan="2" style="text-align:center;" | M5904 Transceiver || colspan="4" style="text-align:center;" | Unused
|-
| 7 || colspan="2" style="text-align:center;" | UNIBUS B Out || colspan="4" style="text-align:center;" | SPC
|-
| 8 || colspan="2" style="text-align:center;" | UNIBUS B In || colspan="4" style="text-align:center;" | SPC
|-
| 9 || colspan="2" style="text-align:center;" | UNIBUS A Out || colspan="4" style="text-align:center;" | SPC
|}

[[Category: MASSBUS Controllers]]
[[Category: UNIBUS Storage Controllers]]