In the 8085 microprocessor, which pair of registers are the dedicated 16 bit registers used for sequencing and stack management?

Introduction / Context:
The Intel 8085 microprocessor has several internal registers, including general purpose registers, the accumulator, and special purpose registers. Among these, the program counter and stack pointer are dedicated 16 bit registers used to control program flow and stack operations. This question checks your understanding of which registers have 16 bit width and what their roles are.

Given Data / Assumptions:

• The 8085 has 8 bit general purpose registers and the accumulator.
• It also has two special 16 bit registers.
• We need to identify the correct pair of 16 bit dedicated registers.

Concept / Approach:
The program counter holds the 16 bit address of the next instruction to be fetched from memory. After each instruction fetch, the program counter is updated to point to the following instruction, unless a control transfer modifies it. The stack pointer holds the 16 bit address of the current top of the stack in memory. Push and pop operations adjust the stack pointer and use it to store or retrieve data from the stack region.

Step-by-Step Solution:
Step 1: Recall that the accumulator and general purpose registers are 8 bit wide in the 8085.Step 2: Recognize that the program counter must address any location in the 64 kilobyte memory space, which requires 16 bits.Step 3: Similarly, the stack pointer must be able to point into memory and is therefore a 16 bit register.Step 4: Match these facts to the option that lists program counter and stack pointer as the dedicated 16 bit registers.

Verification / Alternative check:
Technical descriptions of the 8085 architecture list the register set explicitly. The program counter and stack pointer are described as 16 bit registers, while other registers such as A, B, C, D, E, H, and L are 8 bit each. Although register pairs such as BC, DE, and HL can be used as 16 bit register pairs in some instructions, the question focuses on dedicated registers used for sequencing and stack management, which are PC and SP.

Why Other Options Are Wrong:
Option A: The accumulator is 8 bit, not 16 bit, so pairing it with the program counter is incorrect.Option C: Register H by itself is 8 bit. Only the HL pair can be used as a 16 bit register in some instructions, but HL is not a dedicated control register.Option D: The accumulator is not 16 bits wide; it is an 8 bit register used for arithmetic and logic operations.

Common Pitfalls:
Students sometimes confuse dedicated 16 bit registers with 8 bit registers that can be combined as pairs. While HL, DE, and BC pairs can hold 16 bit values in some instructions, they are not the same as the program counter and stack pointer, which always operate as 16 bit registers and have specific roles in controlling program flow and stack operations.

Final Answer:
The correct answer is Program Counter and Stack Pointer, which are dedicated 16 bit registers.