Data Transfer and Addressing Modes

Instructions and Data Transfer

• A general-purpose instruction transfers a byte or word from register to register, memory to register, register to memory, or with immediate addressing.
• MOV instruction performs tasks such as moving data between registers, moving data between memory and registers, and utilizing immediate addressing.
• Program control transfer instructions facilitate data transfer: from memory to internal register, from internal register to memory, from one register to another, from an input port to internal register, and from internal register to an output port.
• Instructions, except REP, are used to perform rotate operations.
• DAS is not a data copy/transfer function.
• The instruction MOV DS:[2000H], AL copies byte-size data in AX to the memory.

Addressing and Memory

• If CS contains 2001H and IP contains 007CH, the physical memory location accessed for the next instruction is 2008CH.
• Given CS = 2000H and IP = 1000H, the memory address of the next instruction executed by the microprocessor is 21000H.
• If a descriptor has Base = 23000000H, Limit = 012FFH, and G = 1, the described segment ends at 242FFFFFH.
• If the MOD field contains 00, 01, or 10 and the R/M Code is 001, the addressing mode is DS:[BX+DI].
• The starting and ending address of the segment located by the segment register value 1000H : "10000H,1FFFFH".
• The segment-offset combinations that point to a common physical memory address are a) A1B2:000C and c) A1B0:002C.
• In real mode, the physical address accessed by the segment-offset combination 0CD1:02E0 is 0CF0H.
• In calculating the target address to jump to, a displacement is added to the contents of the IP register.
• The instruction MOV AX, 1234H is an example of immediate addressing mode.
• The instruction MOV AX,[BX] exemplifies register indirect addressing mode.

Assembly Instructions and Machine Code

• An assembler is a utility program for converting source code programs from assembly language into machine language.
• For the instruction MOV CL, CH, the code in the REG field when assembled is 001.
• If the direction bit D=1, data flow: to, from. The register REG field the R/M field is located in the second byte of an instruction.
• If the instruction is MOV BL,DS:[1234H], the code for R/M is 110.
• If the instruction is MOV CL,DS:[1234H], the code for mm is 00.
• The instruction MOV [BP], DL will assemble with mm/mod=01.
• The instruction MOV BL,DS:[1234H] will assemble as a 4-byte instruction.
• The machine code for the instruction ADC BX,DX is 13DA in hexadecimal.
• The machine code for the instruction AND AL,0FCH is 24FC in hexadecimal.
• The machine code for the instruction POP BP is 5D in hexadecimal.
• The assembly language equivalent of the machine code 8CD0H is MOVAX,SS.
• The 100010dw mmregr/m template is used for converting assembly instructions to machine code, with the exception of "MOV ES, AX".
• With MOV BL,04Fh and ADDBL, 0B1H, the execution part results in ZF=0 is considered false.

Protected Mode

• A selector value in protected mode provides segment information, except for the ending address.
• Memory protection in protected mode is implemented by restricting access to memory segments through privilege levels and access rights.
• In protected mode, access to the segment is allowed if both RPL = DPL and RPL > DPL.
• 32-bit microprocessors operating in protected mode can address up to 4GB of memory.
• The 80286 could be operated in protected mode, but with only a 24-bit address bus.
• You must never use the segment registers as data registers to hold arbitrary values because: They should only contain segment addresses

Instruction Execution and Flags

• The instruction that performs logical AND operation and the result of the operation is not stored in the destination operand: TEST.
• Opcode selects the operation (addition, subtraction, move, and so on) that is performed by the microprocessor.
• The carry flag acts as the Borrow flag in the instruction SBB.
• CMC inverts the carry flag.
• A MOV [SI], BH instruction writes a byte of data from BH into memory location 1000H assuming SI = 1000H.
• In a compare (CMP) operation, the result of the comparison is not stored anywhere.
• The instruction that performs logical AND operation and the result of the operation is not stored in the destination operand is TEST.
• Given the following, what is the content of the destination after executing the instructions MOVAX, OFEEDH and ANDAX, 0F00Dh is AX =F00Dh.
• Given the following what is the content of the register after executing the instruction MOVAX, 11001100b XORAX, OCH is AX=000Ch.
• In unsigned division of a doubleword in DX AX by a word in CX, the quotient will be placed in AX and the remainder in DX.
• In unsigned division of a word in AX by a byte in DATA2, the quotient will be placed in AL and the remainder in AH.
• In unsigned multiplication of AX with BX, the product will be placed in registers DX;AX.

Bit Manipulation

• Bit Manipulation Instructions is used to shift or rotate bits left or right in register or memory operands.
• It is used to examine the state of individual bits, or groups of bits iand the instruction is Test.
• In the RCL instruction, the carry flag is pushed into LSB & MSB is pushed into the carry flag.