Chapter 6 Summary

Unconditional Jump Instructions

Unconditional Jump Instructions

Short, near, and far jumps allow branching within different byte ranges. Short jump within +127 and -128 bytes, near jump within ±32K bytes, and far jump to any location in the memory system.

Label Field in JMP Instruction

Labels followed by a colon (LABEL:) in JMP instructions indicate the memory location to jump to.

Displacement in Jump Instructions

The distance from the next instruction to the jump location in short or near jumps.

Indirect Jumps

Jumping to the location stored in a register or memory word (near) / doubleword (far) location.

Conditional Jumps

Short jumps based on flag bits (C, Z, O, P, S) with a 16-bit signed displacement in 80386 and above.

Special Conditional Jump (LOOP)

CX decremented and jumps based on conditions like LOOPE, LOOPNE, LOOPZ, and LOOPNZ.

Conditional Set Instructions

Set or clear a byte based on a condition under test in 80386 through Core2.

.IF and .ENDIF Statements

Used in assembly language to generate conditional jump statements for decision-making.

.WHILE and .ENDW Statements

Allow the use of WHILE and REPEAT-UNTIL constructs in assembly language programs.

Procedures

Groups of instructions for a specific task, linked using CALL and returned from using RET instructions.

CALL Instruction

Combines PUSH and JMP, pushing return address and jumping to a procedure.

RET Instruction

Returns from a procedure by removing the return address from the stack.

Interrupts

Software or hardware signals calling procedures, interrupting the current program.

Real Mode Interrupt Vectors

4 bytes long, containing the address of interrupt service procedures.

Handling Interrupts

Flags pushed onto the stack, T and I flags cleared, and jump to interrupt service procedure.

Software Interrupts (INT)

Replace system calls, saving memory space.

IRET Instruction

Used to return from an interrupt service procedure, removing IP, CS, and flags from the stack.

INTO Instruction

Conditional interrupt based on the overflow flag (O).

Interrupt Enable Flag (I)

Controls the INTR pin connection, set by STI and cleared by CLI instructions.

Carry Flag (C)

Controlled by CLC, STC, and CMC instructions.

WAIT Instruction

Tests BUSY or pin, waiting until it becomes logic 1.

LOCK Prefix

Sets the pin to logic 0 during the locked instruction.

BOUND Instruction

Compares register contents with memory boundaries, causing a type 5 interrupt if not within bounds.

ENTER and LEAVE Instructions

Used with stack frames to pass parameters and manage local memory variables.