Avago Technologies LSI53C876E User Manual

Page 207

I/O Instruction

5-17

Initiator Mode

Select Instruction
The LSI53C876 arbitrates for the SCSI bus by asserting
the SCSI ID stored in the

If it loses arbitration, it tries again during the next
available arbitration cycle without reporting any lost
arbitration status.

If the LSI53C876 wins arbitration, it attempts to select the
SCSI device whose ID is defined in the destination ID
field of the instruction. Once the LSI53C876 wins
arbitration, it fetches the next instruction from the address
pointed to by the

DMA SCRIPTS Pointer (DSP)

This way the SCRIPTS can move to the next instruction
before the selection completes. It continues executing
SCRIPTS until a SCRIPT that requires a response from
the Target is encountered.

If the LSI53C876 is selected or reselected before winning
arbitration, it fetches the next instruction from the address
pointed to by the 32-bit jump address field stored in the

DMA Next Address (DNAD)

LSI53C876 to Initiator mode if it is reselected, or to Tar-
get mode if it is selected.

If the Select with SATN/ field is set, the SATN/ signal is
asserted during the selection phase.

Wait Disconnect Instruction
The LSI53C876 waits for the Target to perform a “legal”
disconnect from the SCSI bus. A “legal” disconnect
occurs when SBSY/ and SSEL/ are inactive for a
minimum of one Bus Free delay (400 ns), after the
LSI53C876 receives a Disconnect Message or a
Command Complete Message.

OPC2

OPC1

OPC0 Instruction Defined

Select

Wait Disconnect

Wait Reselect

Set

Clear