User`s manual

Functional Overview
SBCSCSI/D1 2-11
2
Linked CMD Complete
A linked command complete INT instruction interrupt is
generated. This holds the bus in the MSG-IN phase while the
Firmware sets up data structures for the next linked
command. The MPU code restarts the SCRIPTS at an
instruction which clears the SCSI ACK signal to complete the
MSG-IN phase and then waits for the COMMAND phase.
Extended Message
A SCRIPTS instruction clears the SCSI ACK signal to accept
the message byte and then the rest of the message bytes are
received. ACK is not negated for the last message byte.
Instead, an extended message INT instruction interrupt is
generated. The MPU code copies the entire message into the
MSG-IN buffer and then restarts the SCRIPTS at an
instruction which clears the SCSI ACK signal to complete the
MSG-IN phase.
If the extended message was a synchronous data transfer
request, then the Firmware determines the next course of
action. If the received message was a response to a
synchronous data transfer request message, the Firmware
logs the acceptable rate and offset. If the message was
unsolicited, then the Firmware builds a response message
with a rate and offset which is mutually acceptable, and then
restarts the SCRIPTS at an instruction which asserts ATN
before it clears ACK. The assertion of ATN tells the target that
the SIOP has a message (out) ready to transmit in response to
the last message (in).