INSTRUCTION SET DESCRIPTIONS

Table C-4. Instruction Set (Continued)

Name

Description

Operation

Flags

Affected

 

 

 

 

 

 

 

INTO

Interrupt on Overflow:

if

AF –

 

INTO

(OF) = 1

CF –

 

then

DF –

 

Generates a software interrupt if the

 

(SP) ← (SP) – 2

IF –

 

overflow flag (OF) is set; otherwise

 

((SP) + 1:(SP)) ← FLAGS

OF –

 

control proceeds to the following

 

(IF) ← 0

PF –

 

instruction without activating an

 

(TF) ← 0

SF –

 

interrupt procedure. INTO addresses

 

(SP) ← (SP) – 2

TF –

 

the target interrupt procedure (its type

 

((SP) + 1:(SP)) ← (CS)

ZF –

 

is 4) through the interrupt pointer at

 

(CS) ← (12H)

 

 

location 10H; it clears the TF and IF

 

 

(SP) ← (SP) – 2

 

 

flags and otherwise operates like INT.

 

 

((SP) + 1:(SP)) ← (IP)

 

 

INTO may be written following an

 

 

(IP) ← (10H)

 

 

arithmetic or logical operation to

 

 

 

 

 

activate an interrupt procedure if

 

 

 

overflow occurs.

 

 

 

Instruction Operands:

 

 

 

none

 

 

 

 

 

 

IRET

Interrupt Return:

(IP) ← ((SP) + 1:(SP))

AF

 

IRET

(SP) ← (SP) + 2

CF

 

(CS) ← ((SP) + 1:(SP))

DF

 

Transfers control back to the point of

 

(SP) ← (SP) + 2

IF

 

interruption by popping IP, CS, and the

 

FLAGS ← ((SP) + 1:(SP))

OF

 

flags from the stack. IRET thus affects

 

(SP) ← (SP) + 2

PF

 

all flags by restoring them to previously

 

 

SF

 

saved values. IRET is used to exit any

 

 

 

TF

 

interrupt procedure, whether activated

 

 

 

ZF ¸

 

by hardware or software.

 

 

 

Instruction Operands:

 

 

 

none

 

 

 

 

 

 

JA

Jump on Above:

if

AF –

JNBE

Jump on Not Below or Equal:

((CF) = 0) or ((ZF) = 0)

CF –

 

JA disp8

then

DF –

 

(IP) ← (IP) + disp8 (sign-ext to 16 bits)

IF –

 

JNBE disp8

 

 

OF –

 

Transfers control to the target location

 

 

 

PF –

 

if the tested condition ((CF=0) or

 

 

 

SF –

 

(ZF=0)) is true.

 

 

 

TF –

 

Instruction Operands:

 

 

 

ZF –

 

JA short-label

 

 

 

JNBE short-label

 

 

 

 

 

 

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-20

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Intel 80C186XL, 80C188XL Interrupt on Overflow, Interrupt Return, Jump on Above, Jump on Not Below or Equal, JA disp8
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