Question

Question 1 (20 marks) a) Lists the four (4) fields of an assembly language statement of 80386 microprocessor. (2 marks) b) What are the pairs of registers in 80386 microprocessors used to hold the address of instructions in memory? (2 marks) c) What is the output of instruction: ADD AX, (BX+DI] ? (2 marks) d) Give the name of valid registers pairs used to hold the base and offset address of stack operation in 80386 (2 marks) e) Express C17B000016 of a 32-bit floating point number into its equivalent decimal number. (2 marks)

Answer 1

(a) The four fields of an assembly language statement of 80386 microprocessor are

(i) Prefix field - These are used to alter the operation of the instruction. This field may be specified before any instruction.

(ii) Opcode field - This field is used to specify the type of operation to be performed by any instruction.

(iii) Operand field - This field is used to specify the data on which the opearation has to be performed. This data may be the content of a register (Register specifier), this data may be a address location from which the data is to be read (Addressing-mode specifier) or the data may be directly specified in the instruction (Immediate operand).

(iv) Displacement field - This field is used to calculate the address of an operand.

(b) The pair of registers used to hold the address of instructions in memory in case of 80386 microprocessor are CS (Code segment) which is a 16-bit register and EIP which is a 32-bit register. The EIP register is similar to IP (Instruction pointer) as in case of 8086 microprocessor.

(c) The given instruction is ADD AX, [BX+DI]

This is an addition instruction. This instruction is used to add the content of the accumulator (AX) and the content of the memory location whose offset can be calculated by adding the contents of base register (BX) and destination index (DI). After addition, the result will be placed in AX.

(d) The name of the valid register pairs used to hold the base and offset address of stack operation in 80386 microprocessor are Stack Segment Register (SS) and Stack Pointer Register (ESP).