Difference between revisions of "DM11-BB Modem Control Option"

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Revision as of 02:24, 3 October 2019

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 used a custom system unit backplane, containing multiple cards; a flat cable connected this to separate 5-1/4" high rack-mounted dual-height DM11 'distribution panel' backplane. Modular 'line conditioning' units from the DF11 Communications Line Adapter series were installed in the distribution panel to allow support of EIA RS-232 serial lines connected to modems.

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 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 which plugged into the backplane of the DM11 distribution panel. The DM11-BB boards (all dual-width) are:

  • M7246 - Scan
  • M7247 - Data Mux (two)

and 2 single-width, non-DM11-specific cards:

  • M7820 - Interrupt control
  • M105 - Address selection

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) are:

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 are in the last two slots.)

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