LSI53C875 LSI Logic, LSI53C875 Datasheet - Page 212

• Manufacturer Part Number: LSI53C875
• Description: PCI to Ultra SCSI I/O Processor
• Manufacturer: LSI Logic

6-16
Instruction Set of the I/O Processor
Initiator Mode
0
0
0
0
1
Select Instruction
The LSI53C875 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 LSI53C875 wins arbitration, it attempts to select the
SCSI device whose ID is defined in the destination ID
field of the instruction. Once the LSI53C875 wins
arbitration, it fetches the next instruction from the address
pointed to by the
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 LSI53C875 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)
LSI53C875 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 LSI53C875 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
LSI53C875 receives a Disconnect Message or a
Command Complete Message.
OPC2
OPC1
0
0
1
1
0
OPC0
0
1
0
1
0
DMA SCRIPTS Pointer (DSP)
Instruction Defined
Select
Wait Disconnect
Wait Reselect
Set
Clear
SCSI Chip ID (SCID)
register. Manually set the
register.
register.