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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 DMA
SCRIPTS Pointer Save (DSPS) register is used as a
relative offset from the current DMA SCRIPTS Pointer
(DSP) 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