DV11 Communications Multiplexer

The DV11 Communications Multiplexer (also called the DV11 Synchrous Preprocessor) was a UNIBUS multi-line synchronous serial line interface. It supported up to 16 lines, and had a maximum aggregate throughput of 34K characters/second. It used a 'microprocessor' to drive the lines, using 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

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 addresses 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:

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)

NSI	Unused	NSIE	SIE	MCLR	NSOI	MAINT	RIRC	RI	RIE	MEXT		MU			MGO
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

• 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)

Unused				RSEL				Unused				LSEL
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

• 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 hex and quad boards, along with up to two DV11-BA distribution panels (H317-C). Four BC08R flat cables 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 instructions (BRANCH A, BRANCH B, ALU OP, RAM OP, DATA XFR, NPR OP, SET/CLR OP, BCC OP), and an ALU built out of 74 series 74181 ALU 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.)

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:

	Connector
Slot	A	B	C	D	E	F
1	UNIBUS In		M7807
2	M7836
3	M7837
4	M7838
5	M7839
6	M7839
7	M7839
8	M7839
9	UNIBUS Out		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

• DV11 Synchronous Preprocessor Option Bulletin
• DV11 communications multiplexer user's manual
• DV11 communications multiplexer maintenance manual
• DV11 Engineering Drawings