DC11 asynchronous serial line interface
The DC11 asynchronous serial line interface is an early UNIBUS peripheral which provides an asynchronous serial line connection to a modem (Bell 103 and 202 models), using an EIA RS-232 interface. Both input and output used programmed I/O (with separate receive and transmit interrupts); there was no buffering.
The line parameters:
- baud rates (4 speeds, separate for transmit and receive, ranging from 50 to 1800, depending on the clock module )
- character length (5-8 bits)
- output stop bits (1 or 2)
- input parity (even or odd)
could be set under program control. A 'break' condition on the line (i.e. continuous assertion) could also be generated and detected.
The speeds available with various models were:
| Model | Speeds |
|---|---|
| -AA | 300, 150, 134.5, 110 |
| -AB | 1800, 1200, 300, 110 |
| -AC | 1200, 600, 150, 110 |
| -AD | 150, 134.5, 110, 50 |
| -AE | 150, 134.5, 110, 75 |
| -AG | 1200, 300, 150, 134.5 |
| -AH | 1800, 1200, 134.5, 110 |
| -AX | Other (up to 19.6K), 150, 134.5, 110 |
Other DF11 Communications Line Adapters could be used in place of the EIA RS-232 interface card.
Device registers
| Register | Abbreviation | Address |
|---|---|---|
| Receive Status Register | DCRCSR | 774000 |
| Receive Buffer Regist | DCRBUF | 774002 |
| Transmit Status Register | DCTCSR | 774004 |
| Transmit Buffer Register | DCTBUF | 774006 |
The addresses shown are for the first DC11 in a system; additional ones (up to 32 total) are normally set to be at 774010, 774020, etc to 774370.
Implementation
The implementation used a single custom system unit backplane, containing two independent DC11's, each consisting of:
- M794 Interface (quad)
- M7821 - Interrupt control
- M105 - Address selection
- M594 EIA level converter
- M957 data set cable connector
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:
| Connector | ||||||
|---|---|---|---|---|---|---|
| Slot | A | B | C | D | E | F |
| 1 | UNIBUS In | M957 | M594 | M7821 | M105 | |
| 2 | G8000 filter | M454 clock | M794 | |||
| 3 | Power | @ | M794 | |||
| 4 | UNIBUS Out | M957 | M594 | M7821 | M105 | |
@ = M205 for -AD, -AE; M405 for -AX; or blank
Power comes in on a single-width stub card in the A3 slot (as is canonical in the PDP-11/20 generation of PDP-11s).
Further reading
- DC11 Asynchronous Line Interface Engineering Drawings - not online
External links
- DC11 asynchronous line interface manual (DEC-11-HDCD-D)
