DHU11 asynchronous serial line interface

The DHU11 asynchronous serial line interface was a replacement for the UNIBUS DH11. It was not programmatically exactly identical to the DH11, but had all the same basic capabilities: it provided 16 RS-232 asynchronous serial lines, and output used DMA.

The reasons for the replacement of the DH11 are not known, but likely the major one was cost: the DH11 consisted of an entire double system unit backplane, containing multiple cards; the DHU11 was a single card. It had some minor improvements over the DH11 (including a fix for its silo problem), but they seem not significant enough by themselves to warrant its replacement. They included:

• input used a 256-character FIFO buffer (somewhat larger than the original DH11's 64-character one);
• the DHU11 includes several microprocessors, and has extended capabilities, including a diagnostic self-test, and flow control support;
• the DHU11 has the ability to transmit under program control; each line has a 64-character FIFO output buffer.

Implementation

Physically, the DHV11 consisted of a single hex card, the M3105, which plugged into a MUD slot. It connected to a pair of H3029 distribution panels (8 lines each) via BC05L flat cables, two per distribution panel; the BC05L connects to a 40-pin Berg header on each end. The H3029 contains eight male DB-25 connectors (DB-25P).

Device registers

The registers in the DHU11 are somewhat different from those in the DH11:

• it was intended to be program compatible with its QBUS equivalents (the DHV11; and later the DHQ11, which could be set to exactly emulate the DHU11), and since the QBUS has a larger address space than the UNIBUS, it needed two word-sized registers to hold the output buffer address;
• the previously mentioned improvements.

Register	Abbreviation	Address
Control and Status Register	CSR	760020
Receive Buffer Register	RBUF	760022
Receive Timer Register*	RXT	760022
Line Parameter Register	LPR	760024
Transmit FIFO Data Register	TFD	760026
Transmit FIFO Size Register*	TFS	760026
Line Status Register*	STAT	760027
Line Control Register	CTRL	760030
Transmit Buffer Address Register Low	TBADL	760032
Transmit Buffer Address Register Hi	TBADH	760034
Transmit Buffer Count Register	TBCT	760036

Registers marked with a '*' are byte width; the others are all word-width. The RBUF and RXT share an address, as do the TFD and TFS: the RBUF is read only, and the RXT is write only; the TFD is write only, and the TFS and STAT are read only. The LPR through TBCT are replicated, with one for each line in the device; the 'Line' field in the CSR indicates which one is currently available.

The addresses shown are for the first DHU11 in a system; additional ones are normally set to be at 760040, 760060, etc.

Control and Status Register (CSR)

TXA	TXIE	DF	TDE	Tx Line				RDA	RXIE	MR	SKIP	Line
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

• TXA - Transmitter Action
• TXIE - Transmit Interrupt Enable
• DF - Diagnostic Fail
• TDE - Transmit DMA Error
• Tx Line - Line which set TXA
• RDA - Received Data Available
• RXIE - Receiver Interrupt Enable
• MR - Master Reset
• SKIP - Skip Self-Test
• Line - Select LPR through TBCT

Line Parameter Register (LPR)

TSpeed				RSpeed				STOP	EVEN	PARE	CLEN		DICD		Unused
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Line Status Register (STAT)

DSR	Unused	RI	DCD	CTS	Unused		DHU	Not Present
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Line Control Register (CTRL)

Unused			RTS	Unused		DTR	LTYP	MAINT		FXOFF	OAUTO	BREAK	RXE	IAF	TXA
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Further reading

• DHU11 User Guide, EK-DHV11-UG-001