DHV11 asynchronous serial line interface

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The DHV11 asynchronous serial line interface is the first QBUS equivalent to the UNIBUS DH11 (it was later replaced by the DHQ11). It provided 8 RS-232 asynchronous serial lines. Output used DMA (with each line having its own buffer pointer and count); input used a 256-character FIFO buffer.


Physically, the DHV11 consisted of a single quad card, the M3104, connected to a pair of H3173-A distribution panels (4 lines each) via a BC05L flat cable, one per distribution panel; the BC05L connects to a 40-pin Berg header on each end. The H3173-A can be recognized by the DEC part number 50-15588-01 or -02 on its PCB; each contains four male DB-25 connectors (DB-25P). In addition to the usual '-xx' length indicators on the BC05L cable, it was also available in BC05L-1K (21 inch) and BC05L-2F (30 inch) lengths.

Device registers

The registers in the DHQ11 are somewhat different from those in the DH11:

  • the QBUS has a larger address space than the UNIBUS, so it needs two word-sized registers to hold the output buffer address;
  • the DHQ11 includes several microprocessors, and has extended capabilities, including a diagnostic sealf-test, and flow control support;
  • the DHQ11 has the ability to transmit under program control.
Register Abbreviation Address
Control and Status Register CSR 17760440
Receive Buffer Register RBUF 17760442
Transmit Character Register TXC 17760442
Line Parameter Register LPR 17760444
Line Status Register STAT 17760446
Line Control Register CTRL 17760450
Transmit Buffer Address Register Low TBADL 17760452
Transmit Buffer Address Register Hi TBADH 17760454
Transmit Buffer Count Register TBCT 17760456

The RBUF and TXC share an address; the RBUF is read only, and the TXC is write only. The TXC 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 DHV11 in a system; additional ones are normally set to be at 17760460, 17760500.

Control and Status Register (CSR)

TXA TXIE DF TDE Unused Tx Line RDA RXIE MR Unused 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 - Receive Interrupt Enable
  • MR - Master Reset
  • Line - Select TXC through TBCT

Line Parameter Register (LPR)

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)

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

Further reading

  • DHV11 Technical Manual, EK-DHV11-TM-001