DM11-BB Modem Control Option
The DM11-BB Modem Control Option worked with several early UNIBUS asynchronous serial line peripherals to allow the lines to be connected to modems. It could be set to interrupt the CPU when a modem control line (Ring, Carrier, etc) changed state.
The DM11-BB is logically a separate device from the serial line interfaces, albeit one housed in the same backplane. It was used with the DM11, and the DH11 interfaces. Both of these interfaces used a custom system unit backplane, containing multiple cards; flat cables connected this to a separate 5-1/4" high rack-mounted dual-height distribution panel.
There were two different versions of the DM11-BB (unfortunately, there is no accepted naming system for them). The DM11 and early models of the DH11 used the 'early version' of the DM11-BB; it used a DM11 distribution panel backplane. Modular 'line conditioning' units were installed in the distribution panel to allow support of EIA RS-232 serial lines connected to modems.
Later DH11s used the 'new version' of the DM11-BB, which was program-compatible with the early version, but included built-in EIA level conversion, allowing the use of a passive H317-B distribution panel.
DM11-BB Device registers
|Control and Status Register||DMCSR||770500|
|Line Status Register||DMLSR||770502|
The addresses shown are for the first DM11-BB in a system; additional ones (up to 16 total) are normally set to be at 770504, 770510, etc to 770674.
770500: Control and Status Register (DMCSR)
770502: Line Status Register (DMLSR)
The early version of the DH11-BB was connected to the DM11 distribution panel via flat cables which carried the modem control signals, which ran from the M7247 card (two per card) to single-width M971 cards which plugged into the backplane of the DM11 distribution panel (one for each group of 4 lines). The DM11-BB boards (all dual-width) were:
- M7246 - Scan
- M7247 - Data Mux (two)
and 2 single-width, non-DM11-specific cards:
DM11 board locations
(DM11-BB boards were in the last two slots.)
Early DH11 board locations
(DM11-BB boards were in the first two slots.)
Later DM11-BB implementation
The 'later' DM11-BB used two quad-width boards:
- M7807 - Mux and Bus Control
- M7808 - Mux and Modem Scan Control
These boards fitted into the same slots occupied by the DM11-BB boards in the 'early' DH11 versions (the M7807 in slot 1, the M7808 in slot 2). Two flat cables ran from each to the passive distribution panel.