Chaosnet interface

CH11 Unibus board

The Chaosnet UNIBUS interface (also called the CHAOS-11, CH11, QUAD and QAD; there was no generally-used name) and QBCHNI are Chaosnet network interfaces, for the UNIBUS and QBUS respectively. (The two device controllers are identical in programming terms, so they are both covered in this single article.)

They use programmed I/O to transfer data to and from buffers in main memory. They have on-board buffers (one each for inbound and outbound) which can hold one packet of data.

They are both a single quad wire-wrapped card.

Their bus address and interrupt vectors can be set via DIP switches; the defaults are 0764140 and 0270. The network address is also set via a DIP switch.

Device registers

They have 7 registers:

Register	Abbreviation	Address
Command and Status Register	CAICSR	764140
My address (read only)	CAIMYN	764142
Write buffer (write only)	CAIWBF	764142
Read buffer	CAIRBF	764144
Read bit counter	CAIRBC	764146
Unused		764150
Initiate transmission	CAIXMT	764152
Unused		764154
Unused		764156
Load interval timer (write only)	CAITIM	764160

In the register contents (below), bits which are read/write or unused are shown in normal font, those which are read-only are in italics, and those which are write-only are shown in bold.

764140: Control Status Register (CSR)

RDN	ERR	RST	LSTCN				TCL	TDN	TAB	TEN	REN	RCL	SPY	LPBK	TIE
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Bits are:

Bits	Use
RDN	Receive done
ERR	CRC error
RST	I/O reset for interface
LSTCN	Count of messages lost
TCL	Transmitter clear
TDN	Transmitter done
TAB	Transmit aborted by conflict
TEN	Transmit interrupt enable
REN	Receive interrupt enable
RCL	Receiver clear
SPY	Accept all messages
LPBK	Loop back in interface
TIE	Timer interrupt enable (was Transmitter busy)

764142: My Address Register (MYN)

Subnet7 <---> Subnet0								Host7 <---> Host0
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Read-only register.

764142: Write Buffer Register (WBF)

OutData15 <---> OutData00
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Write-only register.

764144: Read Buffer Register (RBF)

InData15 <---> InData0
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Read-only register.

764146: Read Bit Counter Register (RBC)

Unused				BitCount11 <---> BitCount0
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

On the Chaosnet UNIBUS interface, a read-only register.

On the QBCHNI, writing the interface's network address into this register initiates transmission of a packet.

764152: Initiate Transmission Register (XMT)

Subnet7 <---> Subnet0								Host7 <---> Host0
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

On the Chaosnet UNIBUS interface, a read-only register; reading it initiates transmission of a packet. (The data returned is the interface's network address.)

764160: Load Interval Timer Register (TIM)

Timer15 <---> Timer00
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Write-only register.

External links

• CHAOS; - includes drawings and documentation
  • CHS DEFS - register declarations
  • $QUAD LOG - "Log of ChaosNet Interface Boards (quad-high, PDP-11 version)"
  • QUAD SETUP - "how to setup .. Chaosnet Interfaces"
  • QUAD ECO - "ECO to .. Change cable speed to 4 MHz"
  • QADCHS NOTE - random jottings
• SUDS drawings converted to PNG pictures