Jump instructions

They are used to transfer the flow of the process to the indicated

operator.

JMP

JA (JNBE)

JAE (JNBE)

JB (JNAE)

JBE (JNA)

JE (JZ)

JNE (JNZ)

JG (JNLE)

JGE (JNL)

JL (JNGE)

JLE (JNG)

JC

JNC

JNO

JNP (JPO)

JNS

JO

JP (JPE)

JS

JMP INSTRUCTION

Purpose: Unconditional jump.

Syntax:

JMP destiny

This instruction is used to deviate the flow of a program without taking into account the actual conditions of the flags or of the data.

JA (JNBE) INSTRUCTION

Purpose: Conditional jump.

Syntax:

JA Label

After a comparison this command jumps if it is or jumps if it is not down or if not it is the equal.

This means that the jump is only done if the CF flag is deactivated or if the ZF flag is deactivated, that is that one of the two be equal to zero.

JAE (JNB) INSTRUCTION

Purpose: Conditional jump.

Syntax:

JAE label

It jumps if it is or it is the equal or if it is not down.

The jump is done if CF is deactivated.

JB (JNAE) INSTRUCTION

Purpose: Conditional jump.

Syntax:

JB label

It jumps if it is down, if it is not , or if it is the equal.

The jump is done if CF is activated.

JBE (JNA) INSTRUCTION

Purpose: Conditional jump.

Syntax:

JBE label

It jumps if it is down, the equal, or if it is not .

The jump is done if CF is activated or if ZF is activated, that any of them be equal to 1.

JE (JZ) INSTRUCTION

Purpose: Conditional jump.

Syntax:

JE label

It jumps if it is the equal or if it is zero.

The jump is done if ZF is activated.

JNE (JNZ) INSTRUCTION

Purpose: Conditional jump.

Syntax:

JNE label

It jumps if it is not equal or zero.

The jump will be done if ZF is deactivated.

JG (JNLE) INSTRUCTION

Purpose: Conditional jump, and the sign is taken into account.

Syntax:

JG label

It jumps if it is larger, if it is not larger or equal.

The jump occurs if ZF = 0 or if OF = SF.

JGE (JNL) INSTRUCTION

Purpose: Conditional jump, and the sign is taken into account.

Syntax:

JGE label

It jumps if it is larger or less than, or equal to.

The jump is done if SF = OF

JL (JNGE) INSTRUCTION

Purpose: Conditional jump, and the sign is taken into account.

Syntax:

JL label

It jumps if it is less than or if it is not larger than or equal to.

The jump is done if SF is different than OF.

JLE (JNG) INSTRUCTION

Purpose: Conditional jump, and the sign is taken into account.

Syntax:

JLE label

It jumps if it is less than or equal to, or if it is not larger.

The jump is done if ZF = 1 or if SF is defferent than OF.

JC INSTRUCTION

Purpose: Conditional jump, and the flags are taken into account.

Syntax:

JC label

It jumps if there is cartage.

The jump is done if CF = 1

JNC INSTRUCTION

Purpose: Conditional jump, and the state of the flags is taken into

account.

Syntax:

JNC label

It jumps if there is no cartage.

The jump is done if CF = 0.

JNO INSTRUCTION

Purpose: Conditional jump, and the state of the flags is taken into

account.

Syntax:

JNO label

It jumps if there is no overflow.

The jump is done if OF = 0.

JNP (JPO) INSTRUCTION

Purpose: Conditional jump, and the state of the flags is taken into

account.

Syntax:

JNP label

It jumps if there is no parity or if the parity is uneven.

The jump is done if PF = 0.

JNS INSTRUCTION

Purpose: Conditional jump, and the state of the flags is taken into

account.

Syntax:

JNP label

It jumps if the sign is deactivated.

The jump is done if SF = 0.

JO INSTRUCTION

Purpose: Conditional jump, and the state of the flags is taken into

account.

Syntax:

JO label

It jumps if there is overflow.

The jump is done if OF = 1.

JP (JPE) INSTRUCTION

Purpose: Conditional jump, the state of the flags is taken into account.

Syntax:

JP label

It jumps if there is parity or if the parity is even.

The jump is done if PF = 1.

JS INSTRUCTION

Purpose: Conditional jump, and the state of the flags is taken into

account.

Syntax:

JS label

It jumps if the sign is on.

The jump is done if SF = 1.

4.7 Instructions for cycles:loop

They transfer the process flow, conditionally or unconditionally, to a

destiny, repeating this action until the counter is zero.

LOOP

LOOPE

LOOPNE

LOOP INSTRUCTION

Purpose: To generate a cycle in the program.

Syntax:

LOOP label

The loop instruction decreases CX on 1, and transfers the flow of the

program to the label given as operator if CX is different than 1.

LOOPE INSTRUCTION

Purpose: To generate a cycle in the program considering the state of ZF.

Syntax:

LOOPE label

This instruction decreases CX by 1. If CX is different to zero and ZF is equal to 1, then the flow of the program is transferred to the label indicated as operator.

LOOPNE INSTRUCTION

Purpose: To generate a cycle in the program, considering the state of ZF.

Syntax:

LOOPNE label

This instruction decreases one from CX and transfers the flow of the program only if ZF is different to 0.

4.8 Counting instructions

They are used to decrease or increase the content of the counters.

DEC

INC

DEC INSTRUCTION

Purpose: To decrease the operator.

Syntax:

DEC destiny

This operation subtracts 1 from the destiny operator and stores the new

value in the same operator.

INC INSTRUCTION

Purpose: To increase the operator.

Syntax:

INC destiny The instruction adds 1 to the destiny operator and keeps the

result in the same destiny operator.

4.9 Comparison instructions

They are used to compare operators, and they affect the content of the

flags.

CMP

CMPS (CMPSB) (CMPSW)

CMP INSTRUCTION

Purpose: To compare the operators.

Syntax:

CMP destiny, source

This instruction subtracts the source operator from the destiny operator but without this one storing the result of the operation, and it only affects the state of the flags.

CMPS (CMPSB) (CMPSW) INSTRUCTION

Purpose: To compare chains of a byte or a word.

Syntax:

CMP destiny, source

With this instruction the chain of source characters is subtracted from the destiny chain.

DI is used as an index for the extra segment of the source chain, and SI as an index of the destiny chain.

It only affects the content of the flags and DI as well as SI are incremented.

4.10 Flag instructions

They directly affect the content of the flags.

CLC

CLD

CLI

CMC

STC

STD

STI

CLC INSTRUCTION

Purpose: To clean the cartage flag.

Syntax:

CLC

This instruction turns off the bit corresponding to the cartage flag, or in other words it puts it on zero.

CLD INSTRUCTION

Purpose: To clean the address flag.

Syntax:

CLD

This instruction turns off the corresponding bit to the address flag.

CLI INSTRUCTION

Purpose: To clean the interruption flag.

Syntax:

CLI

This instruction turns off the interruptions flag, disabling this way those maskarable interruptions.

A maskarable interruptions is that one whose functions are deactivated when IF=0.

CMC INSTRUCTION

Purpose: To complement the cartage flag.

Syntax:

CMC

This instruction complements the state of the CF flag, if CF = 0 the instructions equals it to 1, and if the instruction is 1 it equals it to 0.

We could say that it only "inverts" the value of the flag.

STC INSTRUCTION

Purpose: To activate the cartage flag.

Syntax:

STC

This instruction puts the CF flag in 1.

STD INSTRUCTION

Purpose: To activate the address flag.

Syntax:

STD

The STD instruction puts the DF flag in 1.

STI INSTRUCTION

Purpose: To activate the interruption flag.

Syntax:

STI

The instruction activates the IF flag, and this enables the maskarable external interruptions ( the ones which only function when IF = 1).

Date: 2014-12-22; view: 881