Register pair used to indicate memory_____.

Question

Examoogle · Accepted Answer

H and L

Explanation: In the Intel 8085 microprocessor, the H-L register pair is specifically designated as the Memory Pointer register pair. It holds the 16-bit address of the memory location currently being accessed during register-indirect addressing mode instructions.

Working Principle: When an instruction uses the 'M' operand (e.g., MOV A, M), the microprocessor looks at the contents of the H and L registers as a concatenated 16-bit memory address. The H register provides the high-order byte and the L register provides the low-order byte. This mechanism allows the programmer to dynamically point to any location in the 64KB address space of the 8085.

Key Formulas: $Address = (H \ll 8) | L$ — Calculation of the 16-bit memory address using the H-L pair

Key Points: The H-L pair functions as a 16-bit address register for memory-related operations.; Instruction set uses 'M' as a mnemonic to represent memory locations pointed by H-L.; It is the only register pair in 8085 that can be used directly for indirect memory addressing.; The 8085 architecture supports a total address space of $2^{16} = 65,536$ bytes.

Advantages: Allows dynamic memory addressing during program execution.; Simplifies data manipulation in arrays or tables within memory.

Disadvantages: Requires two clock cycles to load/store from memory via indirect addressing.; Consumes a general-purpose register pair that could otherwise store temporary data.

Applications: Table look-up operations; String/Array processing; Stack manipulation; Data moving between memory and CPU registers

Additional Info: Option A (B and C) is a general-purpose register pair used for data storage or 16-bit counters.. Option B (D and E) is a general-purpose register pair used for double-precision arithmetic operations like DAD.. Option D (W and Z) are temporary registers used by the internal hardware for arithmetic logic operations and are not accessible to the programmer.

Answer: C is correct — The H and L register pair serves as the primary memory pointer in the Intel 8085 microprocessor.

Exam Tip: Always remember that while B-C, D-E, and H-L are all 16-bit register pairs, H-L is the only one intended for memory addressing in the 8085 instruction set.

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