View source for VDH/11 Very Distant Host Controller

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 driver]]s) is a [[Direct Memory Access|DMA]] [[UNIBUS]] [[synchronous serial line]] [[peripheral]] produced by [[Advanced Computer Communications‎|ACC]] to allow a UNIBUS machine to connect to an [[ARPANET]] [[Interface Message Processor|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 [[cyclic redundancy check|CRC]]."

==Registers==

{| border=1
! 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)===
{{16bit-header}}
| ANYERR || CHKERR || OVERRUN || WCERR || FORMERR || colspan=3 | Unused || READY || INTENB || colspan=2 | Unused || ABRUN || ABSEL || EOT || GO
{{16bit-bitout}}

* 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)===
{{16bit-header}}
| colspan=16 | Data15 <---> Data00
{{16bit-bitout}}

===0767604: Current Word Address In Register (CWAI)===
{{16bit-header}}
| colspan=16 | WA15 <---> WA00
{{16bit-bitout}}

===0767606: Word Count In Register (WCI)===
{{16bit-header}}
| colspan=16 | WC15 <---> WC00
{{16bit-bitout}}

===0767610: Control & Status Out Register (CSRO)===
{{16bit-header}}
| colspan=2 | Unused || OVERRUN || WCERR || colspan=4 | Unused || READY || INTENB || TIMSEL || TIMRUN || EOTINT || TIMINT || Unused || GO
{{16bit-bitout}}

* 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)===
{{16bit-header}}
| colspan=16 | Data15 <---> Data00
{{16bit-bitout}}

===0767614: Current Word Address Out Register (CWAO)===
{{16bit-header}}
| colspan=16 | WA15 <---> WA00
{{16bit-bitout}}

===0767616: Word Count Out Register (WCO)===
{{16bit-header}}
| colspan=16 | WC15 <---> WC00
{{16bit-bitout}}

==External links==

* [https://minnie.tuhs.org/cgi-bin/utree.pl?file=SRI-NOSC/ncpk/drivers drivers] - [[Network UNIX]] device drivers, including VDH/11
** [https://minnie.tuhs.org/cgi-bin/utree.pl?file=SRI-NOSC/ncpk/drivers/net_vdh.h net_vdh.h]
** [https://minnie.tuhs.org/cgi-bin/utree.pl?file=SRI-NOSC/ncpk/drivers/vdh.c vdh.c]
* [https://github.com/pdp11/elf-operating-system/blob/master/files/kdvdh.m11%5Blep%2Cjrl%5D168 KDVDH.M11] - [[ELF operating system|ELF]] VDH/11 device driver
** [https://github.com/pdp11/elf-operating-system/blob/master/files/ktbl.sml%5Blep%2Cjrl%5D168 KTBL.SML] - associated header file

[[Category: 1822 Interfaces‎]]
[[Category: UNIBUS Network Interfaces]]