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 early models of 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 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 a new version of the DM11-BB, which was program-compatible with the early version, but included EIA level conversion, allowing the use of a passive 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 a 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 | M7281 | ||
| 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 DH11 boards
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).
