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INSTRUCTION SET DESCRIPTIONS
C-20
INTO Interrupt on Overflow:
INTO
Generates a software interrupt if the
overflow flag (OF) is set; otherwise
control proceeds to the following
instruction without activating an
interrupt procedure. INTO addresses
the target interrupt procedure (its type
is 4) through the interrupt pointer at
location 10H; it clears the TF and IF
flags and otherwise operates like INT.
INTO may be written following an
arithmetic or logical operation to
activate an interrupt procedure if
overflow occurs.
Instruction Operands:
none
if
(OF) = 1
then
(SP) ← (SP) – 2
((SP) + 1:(SP)) ← FLAGS
(IF) ← 0
(TF) ← 0
(SP) ← (SP) – 2
((SP) + 1:(SP)) ← (CS)
(CS) ← (12H)
(SP) ← (SP) – 2
((SP) + 1:(SP)) ← (IP)
(IP) ← (10H)
AF –
CF –
DF –
IF –
OF –
PF –
SF –
TF –
ZF –
IRET Interrupt Return:
IRET
Transfers control back to the point of
interruption by popping IP, CS, and the
flags from the stack. IRET thus affects
all flags by restoring them to previously
saved values. IRET is used to exit any
interrupt procedure, whether activated
by hardware or software.
Instruction Operands:
none
(IP) ← ((SP) + 1:(SP))
(SP) ← (SP) + 2
(CS) ← ((SP) + 1:(SP))
(SP) ← (SP) + 2
FLAGS ← ((SP) + 1:(SP))
(SP) ← (SP) + 2
AF
CF
DF
IF
OF
PF
SF
TF
ZF
JA
JNBE
Jump on Above:
Jump on Not Below or Equal:
JA
disp8
JNBE
disp8
Transfers control to the target location
if the tested condition ((CF=0) or
(ZF=0)) is true.
Instruction Operands:
JA short-label
JNBE short-label
if
((CF) = 0) or ((ZF) = 0)
then
(IP) ← (IP) + disp8 (sign-ext to 16 bits)
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