LSI 53C810A User Manual
Page 172
6-32
Instruction Set of the I/O Processor
RA
Relative Addressing Mode
23
When this bit is set, the 24-bit signed value in the
register is used as a
relative offset from the current
address (which is pointing to the next instruction,
not the one currently executing). The relative mode does
not apply to Return and Interrupt SCRIPTS.
Jump/Call an Absolute Address
Start execution at the new absolute address.
Jump/Call a Relative Address
Start execution at the current address plus (or minus) the
relative offset.
The SCRIPTS program counter is a 32-bit value pointing
to the SCRIPTS instruction currently under execution by
the LSI53C810A. The next address is formed by adding
the 32-bit program counter to the 24-bit signed value of
the last 24 bits of the Jump or Call instruction. Because
it is signed (2’s complement), the jump can be forward or
backward.
MSG
C/D
I/O
SCSI Phase
0
0
0
Data-Out
0
0
1
Data-In
0
1
0
Command
0
1
1
Status
1
0
0
Reserved
1
0
1
Reserved
1
1
0
Message-Out
1
1
1
Message-In
Command
Condition Codes
Absolute Alternate Address
Command
Condition Codes
Don’t Care
Alternate Jump Offset