LSI53C875 LSI Logic, LSI53C875 Datasheet - Page 227

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

CT
IF
JMP
Transfer Control Instructions
The SCRIPTS program counter is a 32-bit value pointing
to the SCRIPT currently being executed by the
LSI53C875. 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.
A relative transfer can be to any address within a
16 Mbyte segment. The program counter is combined
with the 24-bit signed offset (using addition or
subtraction) to form the new execution address.
SCRIPTS programs may contain a mixture of direct
jumps and relative jumps to provide maximum versatility
when writing SCRIPTS. For example, major sections of
code can be accessed with far calls using the 32-bit
physical address, then local labels can be called using
relative transfers. If a SCRIPT is written using only
relative transfers it does not require any run time
alteration of physical addresses, and could be stored in
and executed from a PROM.
Carry Test
When this bit is set, decisions based on the ALU carry bit
can be made. True/False comparisons are legal, but Data
Compare and Phase Compare are illegal.
Interrupt-on-the-Fly
When this bit is set, the interrupt instruction does not halt
the SCRIPTS processor. Once the interrupt occurs, the
Interrupt-on-the-Fly bit
asserted.
Jump If True/False
This bit determines whether the LSI53C875 branches
when a comparison is true or when a comparison is false.
This bit applies to phase compares, data compares, and
carry tests. If both the Phase Compare and Data
Compare bits are set, then both compares must be true
to branch on a true condition. Both compares must be
false to branch on a false condition.
Command
Don’t Care
(Interrupt Status
Alternate Jump Offset
Condition Codes
(ISTAT), bit 2) is
6-31
21
20
19