View source for DP11-A Synchronous Line Interface

The ''' DP11-A''' is the earliest [[synchronous serial line]] [[peripheral|interface]] for the [[UNIBUS]]; it was double-[[buffer]]ed, and used [[programmed I/O]] (with separate receive and transmit [[interrupt]]s) to transfer data, in either [[half-duplex]] or [[full-duplex]], at [[baud rate]]s up to 50K bits/second.

It was intended to interface to Bell 201, 301 and 303 series [[modem]]s. The [[character]] length (6, 7 or 8 [[bit]]s), and the [[sync character]], were selectable under program control, as were idling (sending the sync character), as well as the modem control leads; the DP11-A can also be set to discard incoming sync characters.

Options allowed extending the character length to 10. 11 or 12 bits, and use of an internal [[clock]].

It was constructed from a number of smaller [[FLIP CHIP]]s, along with a larger [[printed circuit board|board]], which were installed in a custom 4-slot [[backplane]] [[system unit]].

==Registers==

{| border=1
! Register !! Abbreviation !! Address
|-
|Receiver Control and Status Register      || DPRCSR || 774770
|-
|Receiver Buffer Register                  || DPRBUF || 774772
|-
|Sync Register                             || DPSYNC || 774773
|-
|Additional Sync Register                  || DPASYNC || 774777
|-
|Transmitter Control and Status Register   || DPRCSR || 774774
|-
|Transmitter Buffer Register               || DPRBUF || 774776
|}

The two SYNC registers seem to overlay the buffer registers; this is not yet sorted out.

The [[address]]es shown are for the first DP11-A in a system; additional ones are normally set to be at 774760, 774750, etc to 774400.

==Implementation==

The modules are:

* G8000 - +8V Filter
* [[M105]] - UNIBUS Address Selector Module
* M239 - Divide by 16 Module (optional)
* M405 - Clock Module (optional)
* M594 - Level Converter Module
* [[M7820]] - Interrupt Control
* M7065 - Receiver Module (one mandatory, two optional)
* M7075 - Transmitter Module (ditto)
* M7223 - Control Module

The M7223 is a [[DEC card form factor|quad]] card; the others are all single. (Of those, the M796 and M7820 are [[DEC card form factor|extended length]]; the M239 and M405 are standard length.) 

The M594 can be substituted with other adapter cards from the [[DF11 Communications Line Adapter|DF11]] series; in particular, the M595 is used with the Bell 303 series modem. 

Board locations (as seen from the board insertion side of the backplane, not the [[wire-wrap]] pin side, as is common in [[DEC]] documentation) are:

{| class="wikitable"
! !! colspan="6" | Connector
|-
! Slot !! A !! B !! C !! D !! E !! F
|-
| 1 || colspan="2" style="text-align:center;" | UNIBUS In || colspan="4" style="text-align:center;" | M7223
|-
| 2 || G8000 Filter || &nbsp; || M105 || M7820 || M405 || M239
|-
| 3 || Power || &nbsp; || M7075 || M7065 || M7075 || M7065
|-
| 4 || colspan="2" style="text-align:center;" | UNIBUS Out || Modem connector || Level Converter
|}

Power comes in on a single-width stub card in the A3 slot (as is canonical in the [[PDP-11/20]] generation of [[PDP-11]]s).

[[Category:UNIBUS Peripherals]]