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 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 plugged into the distribution panel backplane 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.
Contents
DM11-BB Device registers
| Register | Abbreviation | Address |
|---|---|---|
| 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)
| RING | CARR | CTS | SREC | CLRSC | CLRMUX | MAINT | STEP | DONE | IE | SCEN | Unused | Line | |||
| 15 | 14 | 13 | 12 | 11 | 10 | 09 | 08 | 07 | 06 | 05 | 04 | 03 | 02 | 01 | 00 |
770502: Line Status Register (DMLSR)
| Unused | RING | CARR | CTS | SREC | STX | RTS | DTR | LEN | |||||||
| 15 | 14 | 13 | 12 | 11 | 10 | 09 | 08 | 07 | 06 | 05 | 04 | 03 | 02 | 01 | 00 |
Implementation
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
Board locations in the DM11 backplane (as seen from the board insertion side of the backplane, not the wire-wrap pin side, as is common in DEC documentation) were:
| Connector | ||||||
|---|---|---|---|---|---|---|
| Slot | A | B | C | D | E | F |
| 1 | UNIBUS In | M7240 | ||||
| 2 | M105 | M7241 | ||||
| 3 | Power | M405 | M782 | M782 | M7242 | |
| 4 | M974 Cable | M7245 | ||||
| 1 | M7244 | |||||
| 2 | M7243 | |||||
| 3 | Power | M7247 | M7246 | |||
| 4 | UNIBUS Out | M7247 | M105 | M7820 | ||
(DM11-BB boards were in the last two slots.)
Early DH11 board locations
| Connector | ||||||
|---|---|---|---|---|---|---|
| Slot | A | B | C | D | E | F |
| 1 | UNIBUS In | M7247 | M105 | M7821 | ||
| 2 | M7821 | M796 | M7247 | M7246 | ||
| 3 | M7278 | |||||
| 4 | M7277 | |||||
| 5 | M7289 | |||||
| 6 | M7821 | M405 | M7280 | |||
| 7 | M7360 | M971 | M7280 | |||
| 8 | M7288 | |||||
| 9 | UNIBUS Out | M7279 | M405 | M4540 | ||
(DM11-BB boards were in the first two slots.)
Later DM11-BB implementation
The 'later' DM11-BB used two new quad-width boards (the DH11 backplane, etc, were otherwise identical):
- 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.
