View source for LH-DH/11 Local/Distant Host Controller

The '''LH-DH/11 Local/Distant Host Controller''' was a [[Direct Memory Access|DMA]] [[UNIBUS]] [[1822 interface]] produced by [[Advanced Computer Communications‎|ACC]] to allow a UNIBUS machine to connect to anything that provided a BBN-1822 bit-serial interface; most commonly as [[IMP interface]]s to [[ARPANET]] [[Interface Message Processor|IMPs]], but also to [[Packet Radio Network]] interfaces.

It consisted of a 10-1/2" rack [[mounting box]] holding a pair of [[wire-wrap]]ped boards (one for [[packet]] input, and one for output), holding a number of SSI [[transistor-transistor logic|TTL]] [[integrated circuit]]s; there was also an internal [[power supply]]. Level converters allowed use as either a Local Host or Distant Host 1822 interface; [[BC11A UNIBUS cable|BC11A cables]] connected it to the rest of the system.

==Registers==

{| border=1
! Register !! Abbreviation !! Address
|-
|Control & Status In Register      || CSRI || 0767600
|-
|Data Buffer In Register           || DBRI || 0767602
|-
|Current Word Address In Register  || CWAI || 0767604
|-
|Word Count In Register            || WCI || 0767606
|-
|Control & Status Out Register     || CSRO || 0767610
|-
|Data Buffer Out Register          || DBRO || 0767612
|-
|Current Word Address Out Register || CWAO || 0767614
|-
|Word Count Out Register           || WCO || 0767616
|}

===0767600: Control & Status In Register (CSRI)===
{{16bit-header}}
| ERR || NXM || EOM || Unused || HR || INR || RMRE || IDBF || RDY || IE || colspan=2 | XBA16-17 || SENB || HRC || IRST || GO
{{16bit-bitout}}

* ERR - Error Flag
* NXM - Non-Existent Memory 
* EOM - End of Message
* HR - Host Ready
* INR - IMP Not Ready
* RMRE - Receive Master Ready Error
* IDBF - Input Data Buffer Full
* RDY - Device Ready
* IE - Interrupt Enable
* SENB - Store Enable
* HRC - Host Relay Control
* IRST - Input Interface Reset

===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}}
| ERR || NXM || WC0 || colspan=3 | Unused || TMRE || ODBE || RDY || IE || colspan=2 | XBA16-17 || BBM || ELB || ORST || GO
{{16bit-bitout}}

* ERR - Error Flag
* NXM - Non-Existent Memory
* WC0 - Word Count = 0
* TMRE - Transmit Master Ready Error
* ODBE - Output Data Buffer Empty
* RDY - Device Ready
* IE - Interrupt Enable 
* BBM - Bus-Back Mode
* ELB - Enable Last Bit
* ORST - Output Interface Reset

===0767612: Data Buffer 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}}

==See also==

* [[MLH-DH/LSI11 Multiple Channel Controller]] - [[QBUS]] equivalent

==External links==

* [http://www.bitsavers.org/pdf/advancedComputerCommunications/ACC-LHDH11_Maintenance_Manual_Volume_1_Apr1984.pdf Local/Distant Host Controller LH-DH/11C and LH-DH/11B Maintenance Manual]

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