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C-19
INSTRUCTION SET DESCRIPTIONS
INT Interrupt:
INT
interrupt-type
Activates the interrupt procedure
specified by the interrupt-type
operand. Decrements the stack pointer
by two, pushes the flags onto the
stack, and clears the trap (TF) and
interrupt-enable (IF) flags to disable
single-step and maskable interrupts.
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
(SP) ← (SP) – 2
((SP) + 1:(SP)) ← FLAGS
(IF) ← 0
(TF) ← 0
(SP) ← (SP) – 2
((SP) + 1:(SP)) ← (CS)
(CS) ← (interrupt-type × 4 + 2)
(SP) ← (SP) – 2
((SP) + 1:(SP)) ← (IP)
(IP) ← (interrupt-type × 4)
AF –
CF –
DF –
IF
OF –
PF –
SF –
TF
ZF –
Table C-4. Instruction Set (Continued)
Name Description Operation
Flags
Affected
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