DU11 synchronous serial line interface

The DU11 is an early synchronous serial line interface for the UNIBUS. Like the earlier DP11-A, it used programmed I/O (with separate receive and transmit interrupts) to transfer data; it was double-buffered for both input and output.

It provided an EIA RS-232 interface (to Bell 200 series modems, such as the model 201, and equivalents), and optionally a current loop interface (to Bell 300 series modems, such as the model 303, and equivalents). Baud rates of up to 9.6K bits/second were supported by the EIA interface, and up to 100K bits/second by the current loop interface.

The character length (5, 6, 7 or 8 bits), and the sync character, were selectable; parity (even or odd) was optionally supported for error detection. It could operate in either half-duplex or full-duplex mode. All configuration, as well as all the modem control leads, could be set under program control. A jumper allows configuration of whether one or two contiguous sync characters is needed for synchronization.

It was a quad-width card, the M7822; it plugged into an SPC slot. A Berg header on the card provided the 'native' EIA interface; alternatively, when the M7822 card was plugged into a DD11-B backplane, a two single-card DF11 Communications Line Adapter set could be used to connect to current loop modems which were not supported 'natively' by the M78222 (such as the Bell 303). Optionally, the DFC11-A (installed instead of a DF11) allowed use of an internal clock (when two interfaces were connected directly, without modems)..

Registers

Register	Abbreviation	Address
Receiver Status Register	RxCSR	16xx10
Receiver Data Buffer Register (read only)	RxDBUF	16xx12
Parameter Control Register (write only)	PARCSR	16xx12
Transmitter Status Register	TxCSR	16xx14
Transmitter Data Buffer Register	TxDBUF	16xx16

16xx10: Receiver Status Register (RxCSR)

DSC	RING	CTS	CARR	RACT	SECRCV	DSR	STRSYN	RDN	RIE	DSIE	SRCHSYN	SECXMT	RTS	DTR	Unused
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

• DSC - Data Set Change; set for any change on Ring, Carrier, Data Set Ready, Clear to Send or Secondary Received Data lines
• RING - Ring Indicator
• CTS - Clear to Send
• CARR - Carrier
• RACT - Receiver Active; setting dependent on the internal/external synchronization mode
• SECRCV - Secondary Received Data
• DSR - Data Set Ready
• STRSYN - Strip Sync; sync characters are discarded
• RDN - Receive Done Flag; set when the receive buffer is filled with an assembled character
• RIE - Receiver Interrupt Enable; allows an input interrupt when Receive Done is set
• DSIE - Data Set Interrupt Enable; allows an input interrupt when DSC is set
• SRCHSYN - Search Synchronization; when set, the receiver looks for synch character(s)
• SECXMT - Secondary Transmit Data
• RTS - Request to Send
• DTR - Data Terminal Ready

16xx12 (read): Receiver Data Buffer Register (RxDBUF)

ERR	OVR	Unused	PARERR	Unused				RDBUF
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

• ERR - Error
• OVR - Overrun
• PARERR - Parity Error
• RDBUF - Receiver Data Buffer

16xx12 (write): Parameter Control Register (PARCSR)

Unused		MODE		LEN		PAR EN	EVEN PAR	SYNC
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

• MODE - Synchronous Mode Select (10=External, 11=Internal)
• LEN - Length (00=5, 01=6, 10=7, 11=8)
• PAR EN - Parity Enable
• EVEN PAR - Even Parity selected
• SYNC - Sync Character

16xx14: Transmitter Status Register (TxCSR)

DNA	MD	MCLK	MMS		MBW	Unused	MR	TDN	TIE	DNAIE	SEND	HDFD	Unused		BRK
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

• DNA - Data Not Available
• MD - Maintenance Data
• MCLK - Maintenance Clock
• MMS - Maintenance Mode Select (01=Internal, 10=External, 11=Internal systems)
• MBW - Maintenance Bit Window
• MR - Master Reset
• TDN - Transmitter Done; set when the Transmitter Data Buffer is ready for the next character
• TIE - Transmitter Interrupt Enable; allows a transmit interrupt when Transmit Done is set
• DNAIE - Data Not Available Interrupt Enable
• SEND - Send; enables the transmitter logic
• HDFD - Half-Duplex/Full-Duplex
• BRK - Send Break

16xx16: Transmitter Data Buffer Register (TxDBUF)

Unused								TDBUF
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

• TDBUF - Transmitter Data Buffer

See also

• DUP11 synchronous serial line interface