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 can be stored in and executed from a PROM.

R

Reserved

22

CT

Carry Test

21

 

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.

 

IF

Interrupt-on-the-Fly

20

 

When this bit is set, the interrupt instruction does not halt

 

the SCRIPTS processor. Once the interrupt occurs, the

 

Interrupt-on-the-Fly bit (Interrupt Status One (ISTAT1)

 

 

bit 2) is asserted.

 

JMP

Jump If True/False

19

This bit determines whether the LSI53C875A 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.

5-30

SCSI SCRIPTS Instruction Set

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LSI 53C875A technical manual Bit 2 is asserted, Jmp, Jump If True/False