Machine Language Instructions and Addressing Modes Quiz

Register Addressing

• Any 8-bit register (AH, AL, BH, BL, CH, CL, DH, or DL) or any 16-bit register (AX, BX, CX, DX, SP, BP, SI, or DI) can be addressed.
• The segment registers (CS, DS, ES, or SS) are also addressable for moving data between a segment register and a 16-bit register/memory location or for PUSH and POP.

Segment Registers

• In protected mode, the segment register contains three fields of information.
• The leftmost 13 bits of the segment register address one of 8192 descriptors from a descriptor table.
• The segment register contains a cache portion that is used in protected mode to hold the base address, limit, and access rights acquired from a descriptor.

.MODEL Statement

• The .MODEL statement is used with assembly language to identify the start of a file and the type of memory model used with the file.

Extended Registers

• In the 80386 through the Core2 microprocessors, the extended registers (EAX, EBX, ECX, EDX, ESP, EBP, EDI, and ESI) are also used for register addressing.
• In the 64-bit mode, the registers are RAX, RBX, RCX, RDX, RSP, RBP, RDI, RSI, and R8 through R15.

PUSH and POP Instructions

• Data are transferred between a register or a memory location and the stack by the PUSH and POP instructions.
• Variations of these instructions allow immediate data to be pushed onto the stack, the flags to be transferred between the stack, and all 16-bit registers can transfer between the stack and registers.

Register Sizes

• The 8-bit registers are AH, AL, BH, BL, CH, CL, DH, and DL.
• The 16-bit registers are AX, BX, CX, DX, SP, BP, DI, and SI.
• The 32-bit registers are EAX, EBX, ECX, EDX, ESP, EBP, EDI, and ESI.

Memory Addressing

• By default, all memory-addressing modes address data in the data segment unless BP or EBP addresses memory.
• The BP or EBP register addresses data in the stack segment.
• Direct program memory addressing is allowed with the JMP and CALL instructions to any location in the memory system.

Addressing Modes

• Base relative addressing uses a base register, plus a displacement to access memory data.
• Base relative-plus-index addressing is useful for addressing a two-dimensional memory array.
• Scaled-index addressing is unique to the 80386 through the Core2 and allows accessing words, doublewords, or quadwords in memory arrays.
• Relative program addressing allows a JMP or CALL instruction to branch forward or backward in the current code segment by bytes.
• Indirect program addressing allows the JMP or CALL instructions to address another portion of the program or subroutine indirectly through a register or memory location.