DATA BUS

COMMAND

NVCR

T0-T15

1

2

3

DATA

NDATA

NSYNC

When applicable

7

SCDCT2578 REV B 3/11/98

MODE CODES WITH DATA RECEIVE BROADCAST

1. Valid command word received, contents available on T0-T15 for illegalization purposes. Status must be valid within 600 nS.

2. Valid data word received, contents available on T0-T15. Synchronise data word stored in 32 word data memory.

3. Synchronise data word (when applicable) transferred from 32 word data memory to main memory and available on T0-T15.

REMOTE TERMINAL DETAIL

COMMAND REGISTER

The five most significant bits of the command register contain the

Remote Terminal Address.

Bit 10 of the register is the Transmit / Receive bit. If it is set to '1'

the device will perform the transmit sequence and it is set to '0' it

will perform the receive sequence.

Bits 5 to 9 contain the Subsystem Address but two of these

addresses are reserved and one programable. 11111 (1F) or 00000

(00) indicate that the command is a mode code. The least

significant five bits of the command register are used to decode the

mode code and are not used as the word counter as a mode code

may only have a maximum of one associated word.

111110 (1E) and WRAPEN sets the sequencer up to perform the

wrap around function.

The least significant five bits of the command register contain the

number of data words to be transmitted or received. 11111 is 31

words and 00000 is 32 words.

STATUS REGISTER

ME

Message Error: set internally as a result of an error in the received

message or set externally with a discrete pin to illegalize a

message.

INST

Instrumentation: set to zero.

SR

Service Request: set with a discrete pin.

RESVD

Reserved: set to zero

BCST

Broadcast Command Received: set internally.

BUSY

Subsystem Busy: set with a discrete pin.

SSFL

Subsystem Flag: set with a discrete pin.

DBCA

Dynamic Bus Control Acceptance: set to zero.

TF

Terminal Flag: set with a discrete pin.

The status register is cleared and the external bits loaded on all

commands except 'Transmit Status' and 'Transmit Last Command'.

The external status bits (both discrete and programable) must be

valid 600 nS from the rising edge of NVCR for transmit commands

and mode codes, and 250 nS from the rising edge of NDATA for

the last data word in a receive message.

If discrete status inputs are not used they may be left open circuit.

STATUS RESPONSE TIME

The response time (all commands) measured from the mid bit zero

crossing of the last bit of the last word to the mid bit zero crossing

of the status word sync is nominally 11.0 uS.

This time period is used to monitor for more data words on the bus.

If a valid sync field followed by four valid Manchester bi-phase bits

are detected then this is considered to be another word on the bus.

The response time may be reduced to 6.0 uS (4.0 uS dead bus

time) by setting the MCAIR input active high.

MESSAGE ILLEGALIZATION

Any command or mode command may be illegalized by setting the

NME input active low. The remote terminal will respond with

status with the Message Error bit set, provided the message was

valid, and not use the information received. There will be no

transfers to or from the subsystem.