JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV MICROPROCESSORS AND MICROCONTROLLERS Previous Question Paper (December - 2020 - R16)

The 8086 microprocessor features a 16-bit architecture with a register set categorized into four main groups:

• General Purpose Registers (AX, BX, CX, DX): These are 16-bit registers that can be accessed as two 8-bit registers (e.g., AH/AL). AX is the accumulator, BX acts as a base register for addressing, CX is used for loop counting, and DX is used for I/O operations and multiplication/division.
• Pointer and Index Registers (SP, BP, SI, DI): These 16-bit registers are used for memory addressing. SP (Stack Pointer) and BP (Base Pointer) manage the stack, while SI (Source Index) and DI (Destination Index) are used for string manipulations.
• Segment Registers (CS, DS, SS, ES): These 16-bit registers define the base addresses of the Code, Data, Stack, and Extra segments, respectively, allowing the processor to access up to 1 MB of memory.
• Instruction Pointer (IP) and Status Register (Flags): The IP holds the offset of the next instruction. The 16-bit Flag register contains status flags (CF, PF, AF, ZF, SF, OF) indicating arithmetic results and control flags (TF, IF, DF) for processor operation.

Segmentation is necessary in the 8086 architecture to overcome the limitation of its 16-bit registers while supporting a 20-bit address bus. By dividing the 1 MB physical memory into logical segments of 64 KB each, the processor can address memory using a combination of a 16-bit segment base and a 16-bit offset.

Key advantages include:

• Memory Management: It allows the separation of code, data, and stack areas, which enhances system reliability and prevents code from overwriting data.
• Multitasking Support: Different programs can be loaded into different segments, facilitating easier memory allocation and program relocation.
• Efficiency: It provides a modular approach to memory access, enabling the processor to work with smaller, manageable memory blocks while maintaining a large total address space.