View source for DV11 Communications Multiplexer

The '''DV11 Communications Multiplexer''' (also called the '''DV11 Synchrous Preprocessor''') was a [[UNIBUS]] multi-line [[synchronous serial line]] [[peripheral|interface]]. It supported up to 16 lines, and had a maximum aggregate throughput of 34K [[character]]s/second. It used a 'microprocessor' to drive the lines, using [[Direct Memory Access|DMA]] to the [[PDP-11]]'s [[main memory]] for both input and output.

For [[modem]] control, a single later style [[DM11-BB Modem Control Option‎]] per DV11, mounted in the main DV11 [[backplane]], along with the rest of the DV11 cards, was used. (The DM11-BB is logically a separate device, albeit one housed in the DH11.)

==Registers==

{| border=1
! Register !! Abbreviation !! Address
|-
|System Control Register                 || DVSCR || 775000
|-
|Receiver Interrupt Character Register   || DVRICR || 775002
|-
|Line Control Register                   || DVLCR || 775004
|-
|Secondary Register Selection Register   || DVSRSR || 775006
|-
|Secondary Register Access Register      || DVSRAR || 775010
|-
|Special Functions Register              || DVSFR || 775012
|-
|NPR Status Register                     || DVNSR || 775014
|-
|Modem Control Status Register           || DVMCSR || 775020
|-
|Modem Line Status Register              || DVMLSR || 775022
|}

The [[address]]es shown are for the first DV11 in a system; additional units are normally set to be immediately following (0775040, 0775100, 0775140, etc).

The DV11 has a set of 16 'secondary' registers for each line, access to which is gained by placing the secondary register number and line number in the appropriate bits in the DVSRSR, and then reading/writing the DVSRAR. The secondary registers are:

{| border=1
! Register !! Function
|-
|0 || Transmitter Principal Current Address
|-
|1 || Transmitter Principal Byte Count
|-
|2 || Transmitter Alternate Current Address
|-
|3 || Transmitter Alternate Byte Count
|-
|4 || Receiver Current Address
|-
|5 || Receiver Byte Count
|-
|6 || Transmitter Accumulated Block Check
|-
|7 || Receiver Accumulated Block Check
|-
|10 || Transmitter Control Table Base Address
|-
|11 || Receiver Control Table Base Address
|-
|12 || Line Protocol Parameters
|-
|13 || Line State
|-
|14 || Transmitter Mode Bits
|-
|15 || Receiver Mode Bits
|-
|16 || Line Progress
|-
|17 || Receiver Control Byte Storage
|}

===775000: System Control Register (DVSCR)===

{{16bit-header}}
| NSI || Unused || NSIE || SIE || MCLR || NSOI || MAINT || RIRC || RI ||  RIE || colspan=2 | MEXT || colspan=3 | MU || MGO
{{16bitoctal-bitout}}

* NSI - NPR Status Interrupt
* NSIE - NPR Status Interrupt Enable
* SIE - Storage Interrupt Enable
* MCLR - Master Clear
* NSOI - NPR Status Overflow Interrupt
* MAINT - Maintenance Enable
* RIRC - Receiver Interrupt Response Completed
* RI - Receiver Interrupt
* RIE - Receiver Interrupt Enable
* MEXT - Memory Extension
* MU - Maintenance Use
* MGO - Microprocessor Go

===775006: Secondary Register Selection Register (DVSRSR)===

{{16bit-header}}
| colspan=4 | Unused || colspan=4 | RSEL ||  colspan=4 | Unused || colspan=4 | LSEL
{{16bitoctal-bitout}}

* RSEL - Register Selection
* LSEL - Line Selection

==Implementation==

It was constructed from a custom 9-slot backplane double [[system unit]] ([[DEC part number]] 54-11420), into which were plugged a number of [[DEC card form factor|hex]] and quad [[printed circuit board|boards]], along with up to two DV11-BA [[distribution panel]]s (H317-C). Four BC08R [[flat cable]]s connect the main unit to each  distribution panel (two for data and [[clock]], two for modem control.).

Processing is performed by a 'microprocessor', but this not the kind of device now understood by that term; rather, it is a small custom processor controlled by [[microcode]]. It has 8 different 16-[[bit]] [[instruction]]s (BRANCH A, BRANCH B, ALU OP, RAM OP, DATA XFR, NPR OP, SET/CLR OP, BCC OP), and an [[arithmetic logic unit|ALU]] built out of [[74 series]] 74181 ALU [[integrated circuit|chips]].

===Boards===

The boards in the main unit are:

* M7807 - Mux and Bus Control
* M7808 - Mux and Modem Scan Control
* M7836 - ALU and Transfer Bus
* M7837 - UNIBUS Data and NPR Control
* M7838 - ROM, RAM and Branch
* M7839 - Sync Mux Line Card, 4 lines (up to four cards)

The M7836-M7839 are hex cards; the M7807 and M7808 are quad. (The M7807 and M7808 are shared with the [[DH11 asynchronous serial line interface|DH11]].) 

Board locations (as seen from the board insertion side of the backplanes, 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 In || colspan="4" style="text-align:center;" | M7807
|-
| 2 || colspan="6" style="text-align:center;" | M7836
|-
| 3 || colspan="6" style="text-align:center;" | M7837
|-
| 4 || colspan="6" style="text-align:center;" | M7838
|-
| 5 || colspan="6" style="text-align:center;" | M7839
|-
| 6 || colspan="6" style="text-align:center;" | M7839
|-
| 7 || colspan="6" style="text-align:center;" | M7839
|-
| 8 || colspan="6" style="text-align:center;" | M7839
|-
| 9 || colspan="2" style="text-align:center;" | UNIBUS Out || colspan="4" style="text-align:center;" | M7808
|}

==See also==

* [[DP11-A synchronous serial line interface]]
* [[DU11 synchronous serial line interface]]
* [[DUP11 synchronous serial line interface]]
* [[DQ11 NPR Synchronous Line Interface]]

==External links==

* [http://www.bitsavers.org/pdf/dec/unibus/DV11_Option_Bulletin_Jul75.pdf DV11 Synchronous Preprocessor Option Bulletin]
* [http://www.bitsavers.org/www.computer.museum.uq.edu.au/pdf/EK-DV11-OP-001%20DV11%20Communications%20Multiplexer%20User's%20Manual.pdf DV11 communications multiplexer user's manual]
* [http://www.bitsavers.org/www.computer.museum.uq.edu.au/pdf/EK-DV11-MM-002%20DV11%20Communications%20Multiplexer%20Maintenance%20Manual.pdf DV11 communications multiplexer maintenance manual]
* [http://www.bitsavers.org/pdf/dec/unibus/DV11_Engineering_Drawings_May75.pdf DV11 Engineering Drawings]

[[Category: UNIBUS Synchronous Serial Interfaces]]