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.

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 (ISTAT) bit 2) is

 

asserted.

 

JMP

Jump If True/False

19

 

This bit determines whether the LSI53C810A 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.

 

 

Result of

 

Bit 19

Compare

Action

 

 

 

0

False

Jump Taken

0

True

No Jump

1

False

No Jump

1

True

Jump Taken

 

 

 

Transfer Control Instructions

6-33

Page 173
Image 173
LSI 53C810A technical manual Jmp, Jump If True/False