JNTU B.Tech III MICROPROCESSORS AND MICROCONTROLLERS Previous Question Paper (January/February - 2021 - R16)

The 8086 microprocessor features a 16-bit internal architecture consisting of 14 registers, categorized into General Purpose, Segment, and Status/Pointer registers.

1. 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 the counter for loops/strings, and DX is used for I/O operations and multiplication/division.
2. Pointer and Index Registers (SP, BP, SI, DI): SP (Stack Pointer) points to the top of the stack; BP (Base Pointer) provides a base address for stack data; SI (Source Index) and DI (Destination Index) are used for string manipulation.
3. Segment Registers (CS, DS, SS, ES): These 16-bit registers hold the base addresses for Code, Data, Stack, and Extra segments respectively, enabling 1MB of addressable memory.
4. Instruction Pointer (IP): Holds the offset address of the next instruction to be executed.
5. Flag Register: A 16-bit register containing 9 active flags (6 status flags like Carry, Zero, Sign, Parity, Auxiliary Carry, Overflow; and 3 control flags: Trap, Interrupt, Direction) to indicate the processor status.

• DT/R (Data Transmit/Receive): This output pin indicates the direction of data flow through the data bus buffers. When high, the processor is transmitting data; when low, it is receiving data.
• READY: This input pin is used by slow peripherals or memory to signal the processor that they are ready for data transfer. If low, the processor enters wait states until the signal goes high.
• INTA (Interrupt Acknowledge): This output signal is sent by the processor in response to an interrupt request on the INTR pin, indicating that the processor is ready to receive an interrupt vector number.
• M/IO (Memory/Input-Output): This status pin distinguishes between memory and I/O operations. A high level indicates a memory access, while a low level indicates an I/O port access.