VDH/11 Very Distant Host Controller

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The VDH/11 Very Distant Host Controller (VDH-11 has been seen in contemporaneous documents as the name, but this is probably not correct; no documentation has survived - the information below has been gathered by examining extant device drivers) is a DMA UNIBUS synchronous serial line peripheral produced by ACC to allow a UNIBUS machine to connect to an ARPANET IMP, using the 'Very Distant Host' interface specification.

It was described in one contemporaneous ad as:

"Full-duplex DMA error-checking communications unit [which] connects a PDP-11 to an ARPANET IMP. Sends and receives bisync mode. Provides dual-buffered DMA on input and real time clock. For use on ARPA-style networks using 24-bit or 16-bit CRC."

Registers

Register Abbreviation Address
Command & Status In Register CSRI 0767600
Data Buffer In Register DBRI 0767602
Current Word Address In Register CWAI 0767604
Word Count In Register WCI 0767606
Command & Status Out Register CSRO 0767610
Data Buffer Out/Clock Register DBRO 0767612
Current Word Address Out Register CWAO 0767614
Word Count Out Register WCO 0767616

0767600: Control & Status In Register (CSRI)

ANYERR CHKERR OVERRUN WCERR FORMERR Unused READY INTENB Unused ABRUN ABSEL EOT GO
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
  • ANYERR - Some kind of VDH error
  • CHKERR - Checksum error
  • OVERRUN - Overrun error
  • WCERR - Word count error
  • FORMERR - Packet format error
  • READY - VDH ready
  • INTENB - Interrupt enable
  • ABRUN - Buffer A/B running
  • ABSEL - Select buffer A/B [A=0] /
  • EOT - Packet copied into core
  • GO - Start channel

0767602: Data Buffer In Register (DBRI)

Data15 <---> Data00
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

0767604: Current Word Address In Register (CWAI)

WA15 <---> WA00
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

0767606: Word Count In Register (WCI)

WC15 <---> WC00
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

0767610: Control & Status Out Register (CSRO)

Unused OVERRUN WCERR Unused READY INTENB TIMSEL TIMRUN EOTINT TIMINT Unused GO
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
  • OVERRUN - Overrun error
  • WCERR - Word count error
  • READY - VDH ready
  • INTENB - Interrupt enable
  • TIMSEL - Timer select
  • TIMRUN - Timer run, i.e. enable
  • EOTINT - EOT caused interrupt
  • TIMINT - Timer caused interrupt
  • GO - Start channel

0767612: Data Buffer/Clock Out Register (DBRO)

Data15 <---> Data00
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

0767614: Current Word Address Out Register (CWAO)

WA15 <---> WA00
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

0767616: Word Count Out Register (WCO)

WC15 <---> WC00
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

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