RX

CMD

DATA DATA

DATA

*

STATUS

RX

CMD

DATA

*

STATUS

STATUS

TX

CMD

*

9

SCDCT2578 REV B 3/11/98

Error Conditions

Action taken by device

1. Invalid command.

No response.

Command ignored.

2. Command followed by

No status response.

another word.

Set message error.

Sequence terminated.

3. Broadcast address.

No status response.

Set message error.

Set broadcast.

Sequence terminated.

4. Too few NSSTRB from

Message truncated.

subsystem.

5.Too many NSSTRB from

Bit 1 of BIT register set.

subsystem.

Too many data words will

not be transmitted.

Note: Sequence terminated - termination will take place before

signal NCMDSTRB becomes active, therefore no transfers to /

from subsystem will occur.

BC TO RT TRANSFER

If a valid command is received to receive up to 32 data words and

the second word is another command word then an RT to RT

transfer has been set up (see RT to RT transfer).

All valid data words received are stored in the data buffer memory

until message validation is complete after which the device will

respond with Status.

If the command was a broadcast the status transmission will be

suppressed and the broadcast bit in the status register set.

Data words are also available on T0-T15 as they are received

indicated by signal NDATA.

Only after the message has been completely validated will the data

be transferred to the subsystem in a single burst at 500 nS per

word. This ensures that only complete validated messages are

transferred to the subsystem.

When a complete validated message is stored in the data buffer

memory the signal NCMDSTRB goes low for 8.5 uS synchronized

to the 1 MHZ clock indicating that a completely validated message

has been received. The receive Command word appears on T0-T15

at this time.

If the Busy bit of the Status is set the sequence will terminate after

NCMDSTRB.

The end of the NCMDSTRB will initiate the DMA cycle to transfer

the data words from the data buffer memory to the subsystem. The

first word received is enabled onto T0-T15 and the signal

NDATAST is pulsed low. This sequence is repeated for each data

word that was received.

Error Conditions

Action taken by device

1. Invalid command.

No response.

Command ignored.

2. Invalid data word.

No status response.

Set message error.

Sequence terminated.

3. Non contiguous data.

No status response.

Set message error.

Sequence terminated.

4. Too few data words.

No status response.

Set message error.

Sequence terminated.

5. Too many data words.

No status response.

Set message error.

Set broadcast.

Sequence terminated.

Note: Sequence terminated - termination will take place before

signal NCMDSTRB becomes active, therefore no transfers to /

from subsystem will occur.

RT TO RT TRANSFER

To initiate an RT to RT transfer the Bus Controller will send a

receive command to RTA followed contiguously by a transmit

command to RTB.

RTB will respond with status and contiguous data (see RT to BC

transfer).

RTA (the receiving terminal) will receive the status and data

transmitted by RTB and store the received data in the data buffer

memory until the entire RT to RT transfer has been validated, after

which it will respond with its own status provided it was not a

broadcast command, in which case the status transmission will be

suppressed and the broadcast bit set. It will then transfer the data

to the subsystem (see BC to RT transfer).

The error detection for the transmitting terminal will be the same

as for RT to BC transfer. The error detection for the receiving

terminal is as follows:-