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, ranging from 50 to 1800, depending on the clock module)
• character length (5-8 bits)
• stop bits (1 or 2)
• input parity (even or odd)

could be set under program control (identical for transmit and receive). 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

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