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 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

External links

• drivers - Network UNIX device drivers, including VDH/11
  • net_vdh.h
  • vdh.c
• KDVDH.M11 - ELF VDH/11 device driver
  • KTBL.SML - associated header file