Assembly Language Instructions & Functions

General Purpose Instruction

• A general-purpose instruction transfers a byte or word from register to register.
• Can transfer data from memory to register or vice versa.
• Can use immediate addressing.

Program Control Transfer Instructions

• Transfer data from memory to an internal register.
• Transfer data from one register to another.
• Move data from an input port to an internal register.
• Move data from an internal register to an output port.

Rotate Operations

• ROL (Rotate Left), ROR (Rotate Right), and RCR are instructions used to perform rotate operations.
• REP is not used to perform rotate operations.

Data Copy/Transfer Functions

• MOV (Move) and PUSH are data copy/transfer function.
• DAS is not a data copy/transfer function.

Assembler

• Assembler serves as a utility program.
• It converts source code programs from assembly language into machine language.

Memory Location Access

• If CS contains 2001H and IP contains 007CH, the physical memory location accessed for the next instruction is 2008CH.

Assembling MOV CL, CH instruction

• For the instruction MOV CL, CH, the code in the REG field when assembled is 001.

Memory Address of Next Instruction

• Given CS = 2000H and IP = 1000H, the memory address of the next instruction executed by the microprocessor is 21000H.

MOV [SI], BH Instruction

• If SI = 1000H, MOV [SI], BH writes a byte of data from BH into memory location 1000H

Descriptor Base and Limit

• If a descriptor has Base = 23000000H, Limit = 012FFH, and G = 1, the described segment ends at 242FFFFFH

Addressing Mode

• If the MOD field contains 00, 01, or 10 and the R/M Code is 001, the addressing mode is DS:[BX+DI].

Direction Bit in Instructions

• If the direction bit D=1, data flows "to, from" the register REG field to the R/M field located in the second byte of an instruction.

Code for R/M in MOV BL,DS:[1234H]

• If the instruction is MOV BL,DS:[1234H], the code for R/M = 110.

Code for mm in MOV CL,DS:[1234H]

• If the instruction is MOV CL,DS:[1234H], the code for mm = 00.

Compare (CMP) Operation

• During a compare (CMP) operation, the result of the comparison is not stored.

Selector Value in Protected Mode

• In protected mode, the ending address is not segment information from a selector value.

Memory Protection in Protected Mode

• In protected mode memory, protection is implemented by restricting access to memory segments through both privilege levels and access rights.

Access to Segment in Protected Mode

• In protected mode, access to the segment is allowed if both RPL = DPL and RPL > DPL

Physical Address in Real Mode

• In real mode, the physical address accessed by the segment-offset combination 0CD1:02E0 is 0CF01H.

RCL Instruction

• In the RCL instruction, the carry flag is pushed into the LSB, and the MSB is pushed into the carry flag.

Examining State of Bits

• The TEST instruction is used to examine the state of individual bits or groups of bits.

Microprocessor Operation Selection

• The Opcode selects the operation (addition, subtraction, move, etc.) that is performed by the microprocessor.

Borrow Flag

• The carry flag acts as the Borrow flag in the SBB instruction.

MOV DS:[2000H], AL Instruction

• The instruction MOV DS:[2000H], AL copies a byte-size data in AX to the memory.

MOV [BP],DL Assembly

• The instruction MOV [BP], DL will assemble with mm/mod= 01

Instruction Length

• MOV BL,DS:[1234H] assembles as a 4-byte instruction.

MOV AX, 1234H Example

• MOV AX, 1234H exemplifies immediate addressing mode.

MOV AX,[BX] Example

• MOV AX,[BX] is an example of register indirect addressing mode.

CMP Instruction

• To compare the source and destination operands, the CMP instruction performs subtraction between the operands.

Segment Register and Addressing

• With a segment register value of 1000H, the segment starts at 10000H and ends at 1FFFFH.

Common Physical Memory Address

• The segment:offset combinations a) A1B2:000C, c) A1B0:002C, and d) A1B1:001C point to a common physical memory address.

Memory Addressing with 32-bit Microprocessors

• 32-bit microprocessors operating in protected mode can address up to 4GB of memory.

Address Bus for 80286 in Protected Mode

• The 80286 can be operated in protected mode but only has a 24-bit address bus.

Machine Code Conversion

• 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.

Assembly Language Conversion

• The assembly language equivalent of the machine code 8CD0H is MOVAX, SS.

Execution Results

• Given the instructions MOV BL,04Fh and ADDBL, 0B1H, the execution results in ZF=0 evaluating to False.

Register Content After Instructions

• Given the instructions:
  • MOVAX, 0FEEDH
  • ANDAX, 0F00DH
• The final content of register AX will be F00Dh

Content of Register After Instruction

• Given the instructions MOVAX, 11001100b and XORAX, OCH, the content of register AX after executing the instructions is 000Ch.

Target Address Calculation

• In calculating the target address to jump to, a displacement is added to the contents of the IP register.

Division

• In unsigned division of a doubleword in DX AX by a word in CX, the quotient is placed in AX, and the remainder is put in DX.
• In unsigned division of a word in AX by a byte in DATA2, the quotient is placed in AL and remainder in AH.

Unsigned Multiplication

• In unsigned multiplication of AX with BX, the product is placed in registers DX;AX.

Multiplication Fact

• The statement "In unsigned multiplication of CX with a byte in AL, the product is placed in both AX and DX registers" is False.

Segment Registers

• Segment registers should only contain segment addresses.

Assembly Instructions and Machine Code

• The 100010dw mmregr/m template should be used for converting the assembly instructions to machine code except for "MOV ES, AX".

Logical AND Instruction

• The instruction that performs a logical AND operation without storing the result in the destination operand is TEST.

Inverting the Carry Flag

• The instruction CMC inverts the carry flag.

Bit Manipulation Instructions

• Bit Manipulation Instructions are used to shift or rotate bits left or right in register or memory operands.