Module Comparisons Third-Party Products Functional Information

Asynchronous Serial Modules


There are two types of asynchronous serial modules available for Q-bus systems. The first type is the single and multiport serial line unit (SLU) module, which contains discrete serial line units. The second type is the asynchronous serial multiplexer module.

Serial line units are standalone devices that are managed individually and serviced directly by the processor. The processor console must be a serial line unit. These units should be used sparingly in multiuser systems, due to the load they can place on the processor.

Multiplexers contain a number of serial channels, that are managed together as a unit. These modues have large first-in, first-out (FIFO) buffers, and some support DMA transfers. These features reduce the load on the processor. Multiplexers should be used in multiuser systems that need to support lots of terminals, printers, modems and machine-to-machine connections.

Serial Line Units

The table below contains a comparison of the available SLU modules.

Module Number M7940 M8017 M8028 M8043 M8047 M7195
Model Number DLV11 DLV11-E DLV11-F DLV11-J MXV11-A MXV11-B
Introduced 1975 1977 1977 1978 1980 1983
Discontinued 1981
Board Size Dual Dual Dual Dual Dual Dual
Q-bus Address Size 18-bits 18-bits 18-bits 18-bits 18-bits 22-bits
Serial Ports 1 1 1 4 2 2
UART Type AY-5-1013A AY-5-1013A AY-5-1013A 6402 6402 DC319
Console Compatible yes yes yes yes1 yes2 yes2
Modem Control no yes no no no no
Current Loop yes no yes no no no
Maximum Bit Rate 9600 9600 9600 38400 38400 38400
Split Tx/Rx Clocks no yes yes no no no
Programmable Bit Rate no yes yes no no yes
Receiver Active Bit no yes yes no no yes
Modem Status Bit yes no no no no no
Maintenance bit no yes yes no no yes
Error Flags no yes yes yes yes yes
Boot on Framing Error no yes yes yes1 yes2 yes2
AC Bus Load 2.5 1 1 1 2 2.3
DC Bus Load 1 1 1 1 2 0.5
+5V Load 1.0 A 1.0 A 1.0 A 1.0 A 1.2 A 3.5 A
+12V Load 0.18 A 0.15 A 0.15 A 0.25 A 0.01 A 0.06 A

1 SLU 3 only.
2 SLU 1 only.


The table below contains a comparison of different asynchronous serial multiplexer modules available.

Module Number M7957 M3106 M3104 M3107
Model Number DZV11 DZQ11-M DHV11-A DHQ11-M
Introduced 1977 1985 1984 1987
Board Size Quad Dual Quad Dual
Q-bus Address Size 18-bits 18-bits 22-bits 22-bits
Serial Channels 4 4 8 8
Onboard Processor no no yes yes
UART Type 6402 DC367B SC2681 OCTART
Modem Control limited3 limited3 yes yes
Maximum Bit Rate 96001 96001 38400 38400
Split Tx/Rx Clocks no no yes no
Programmable Bit Rate yes yes yes yes
Auto Flow Control no no yes yes
Maximum Throughput (CPS4) 10970 10970 15000 60000
DMA Support no no yes yes
Halt/Reset on Break no yes2 no no
AC Bus Load 1.26 1.5 2.9 3.2
DC Bus Load 1.0 1.0 1.0 0.5
+5V Load 1.15 A 1.10 A 4.25 A 1.90 A
+12V Load 0.390 A 0.236 A 0.400 A 0.300 A

1 Also supports the non-standard bit rate of 19,800 bps.
2 Line 3 only.
3 Can control the DTR output, which can also be jumpered to RTS. Can detect the Ring Indicator and Carrier Detect inputs.
4 Characters per second.


Any of the SLU modules are a good choice. The backplane real estate will likely be one of the primary factors in choosing one of these modules.

Of the multiplexer modules, the M3107 is the top performer, with a fast onboard processor that provides block mode DMA support. It can also overwhelm a system when receiving high volumes of data from connected devices.

The DZ-series of multiplexers are based on the older UNIBUS DZ11 multiplexer, so they tend to have better software support.


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