INSTRUCTION SET DESCRIPTIONS

Table C-4. Instruction Set (Continued)

Name

Description

Operation

Flags

Affected

 

 

 

 

 

 

 

INT

Interrupt:

(SP) (SP) – 2

AF –

 

INT interrupt-type

((SP) + 1:(SP)) FLAGS

CF –

 

(IF) 0

DF –

 

Activates the interrupt procedure

 

(TF) 0

IF

 

specified by the interrupt-type

 

(SP) (SP) – 2

OF –

 

operand. Decrements the stack pointer

 

((SP) + 1:(SP)) (CS)

PF –

 

by two, pushes the flags onto the

 

(CS) (interrupt-type × 4 + 2)

SF –

 

stack, and clears the trap (TF) and

 

(SP) (SP) – 2

TF ¸

 

interrupt-enable (IF) flags to disable

((SP) + 1:(SP)) (IP)

ZF –

 

single-step and maskable interrupts.

 

(IP) (interrupt-type × 4)

 

 

The flags are stored in the format used

 

 

 

 

 

by the PUSHF instruction. SP is

 

 

 

decremented again by two, and the CS

 

 

 

register is pushed onto the stack.

 

 

 

The address of the interrupt pointer is

 

 

 

calculated by multiplying interrupt-

 

 

 

type by four; the second word of the

 

 

 

interrupt pointer replaces CS. SP

 

 

 

again is decremented by two, and IP is

 

 

 

pushed onto the stack and is replaced

 

 

 

by the first word of the interrupt pointer.

 

 

 

If interrupt-type = 3, the assembler

 

 

 

generates a short (1 byte) form of the

 

 

 

instruction, known as the breakpoint

 

 

 

interrupt.

 

 

 

Instruction Operands:

 

 

 

INT immed8

 

 

 

 

 

 

NOTE: The three symbols used in the Flags Affected column are defined as follows:

the contents of the flag remain unchanged after the instruction is executed ¸? the contents of the flag is undefined after the instruction is executed

the flag is updated after the instruction is executed

C-19

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Intel 80C188XL, 80C186XL user manual Interrupt, INT interrupt-type