LSI 53C875A User Manual
Transfer Control Instructions
5-29
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 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.
(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.
relative offset.
The SCRIPTS program counter is a 32-bit value pointing
to the SCRIPTS currently under execution by the
LSI53C875A. 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
to the SCRIPTS currently under execution by the
LSI53C875A. 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
Table 5.5
SCSI Phase Comparisons
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