8085 register-pair encoding — match bit patterns to register pairs List I (Bit pattern) A. 00 B. 01 C. 10 D. 11 List II (Register pair) 1. SP 2. B–C 3. D–E 4. H–L

Introduction / Context:
Many 8085 instructions encode a register pair with a 2-bit field (rp). Knowing this mapping is essential for decoding opcodes (e.g., LXI rp, DAD rp, INX rp) and writing assemblers/disassemblers.

Given Data / Assumptions:

• We use the conventional 8085 mapping for register pairs in instructions that accept rp.
• The four register pairs are B–C, D–E, H–L, and SP.

Concept / Approach:
Intel’s encoding assigns 00→BC, 01→DE, 10→HL, and 11→SP for the rp field. We simply pair each 2-bit code with its register pair.

Step-by-Step Solution:

Verification / Alternative check:
Check the opcode table: e.g., LXI rp uses opcodes 00xx1001 with rp in bits 5–4; decoding examples confirm the mapping above.

Why Other Options Are Wrong:

• Any option that swaps SP with HL or DE with BC would misdecode popular instructions like DAD H or INX D.

Common Pitfalls:
Confusing the rp mapping with the r (3-bit) single-register field used in MOV/MVI/ADD; they are different encodings.

Final Answer:
A-2, B-3, C-4, D-1