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8085 Register Pairing for 16-Bit Operations: Why Register E Pairs with Register D

8085 Register Pairing for 16-Bit Operations: Why Register E Pairs with Register D

Verified Sources
May 19, 2026

In the Intel 8085, the six general-purpose registers are B, C, D, E, H, and L, and they can be combined only as the fixed register pair sets BC, DE, and HL for 16-bit operations.2 Therefore, register E is paired with register D, making the correct answer:

(iv) D.2

This is not an arbitrary pairing. In the 8085 architecture, the programmer cannot freely combine any two 8-bit registers; only the hardware-defined pairs BC, DE, and HL are valid. As a result, E does not pair with A, B, or C for standard 16-bit register-pair instructions.2

A useful way to remember this is:

8-bit RegistersValid 16-bit Pair
B + CBC
D + EDE
H + LHL

The accumulator A is a special-purpose register and is not part of these standard general-purpose 16-bit pairs.2

Footnotes

  1. Register Set of 8085 - PDF explaining that the only possible 8085 register pairs are BC, DE, and HL, and that they are used for 16-bit operations. ↩ ↩2 ↩3 ↩4

  2. Registers of 8085 microprocessor - GeeksforGeeks - Overview of 8085 registers, including general-purpose registers and valid 16-bit pairings. ↩ ↩2 ↩3

  3. Registers in 8085: Definition, Types, Application & 16 Bit Registers - Testbook - Notes that register E is typically paired with D and lists BC, DE, and HL as valid pairs. ↩

  4. Intel 8085 - Wikipedia - Describes the 8085 as an 8-bit processor with 16-bit operations supported through register pairs BC, DE, and HL, plus SP. ↩

Types of Registers in 8085 | Accumulator | General Purpose Register

Direct Answer

For 16-bit operations in the 8085, register E pairs with register D, forming the DE register pair.2

Footnotes

  1. Register Set of 8085 - PDF explaining that the only possible 8085 register pairs are BC, DE, and HL, and that they are used for 16-bit operations. ↩

  2. Registers in 8085: Definition, Types, Application & 16 Bit Registers - Testbook - Notes that register E is typically paired with D and lists BC, DE, and HL as valid pairs. ↩

To understand why D is correct, it helps to distinguish between 8-bit storage and 16-bit storage in the 8085. Each of the general-purpose registers B, C, D, E, H, and L individually stores 8 bits. When the processor needs to handle a 16-bit value, it combines two predefined 8-bit registers into one logical unit.2

These fixed combinations are central to several instruction types such as LXI (load immediate into a register pair), INX (increment register pair), DCX (decrement register pair), and DAD (double add to HL), all of which operate on valid 16-bit register pairs such as BC, DE, and HL.2 Since DE is one of the official pairs, E must be matched with D—not with A, B, or C.2

This detail frequently appears in computer architecture and microprocessor examinations because it tests whether the learner understands architectural constraints rather than memorizing isolated register names.2

Footnotes

  1. Register Set of 8085 - PDF explaining that the only possible 8085 register pairs are BC, DE, and HL, and that they are used for 16-bit operations. ↩ ↩2

  2. Registers of 8085 microprocessor - GeeksforGeeks - Overview of 8085 registers, including general-purpose registers and valid 16-bit pairings. ↩ ↩2

  3. Registers in 8085: Definition, Types, Application & 16 Bit Registers - Testbook - Notes that register E is typically paired with D and lists BC, DE, and HL as valid pairs. ↩ ↩2

  4. Intel 8085 - Wikipedia - Describes the 8085 as an 8-bit processor with 16-bit operations supported through register pairs BC, DE, and HL, plus SP. ↩ ↩2

How to Solve This MCQ Correctly

  1. 1
    Step 1

    The question refers to classic 8-bit microprocessor register pairing rules, specifically the 8085 register organization where 16-bit pairings are predefined.2

    Footnotes

    1. Register Set of 8085 - PDF explaining that the only possible 8085 register pairs are BC, DE, and HL, and that they are used for 16-bit operations. ↩

    2. Registers of 8085 microprocessor - GeeksforGeeks - Overview of 8085 registers, including general-purpose registers and valid 16-bit pairings. ↩

  2. 2
    Step 2

    The only valid 16-bit general-purpose register pairs are BC, DE, and HL.2

    Footnotes

    1. Register Set of 8085 - PDF explaining that the only possible 8085 register pairs are BC, DE, and HL, and that they are used for 16-bit operations. ↩

    2. Registers in 8085: Definition, Types, Application & 16 Bit Registers - Testbook - Notes that register E is typically paired with D and lists BC, DE, and HL as valid pairs. ↩

  3. 3
    Step 3

    Within the valid pair list, E appears only in DE.2

    Footnotes

    1. Register Set of 8085 - PDF explaining that the only possible 8085 register pairs are BC, DE, and HL, and that they are used for 16-bit operations. ↩

    2. Registers in 8085: Definition, Types, Application & 16 Bit Registers - Testbook - Notes that register E is typically paired with D and lists BC, DE, and HL as valid pairs. ↩

  4. 4
    Step 4

    Because E belongs to DE, its paired register is D.

    Footnotes

    1. Register Set of 8085 - PDF explaining that the only possible 8085 register pairs are BC, DE, and HL, and that they are used for 16-bit operations. ↩

  5. 5
    Step 5

    A is the accumulator, while B pairs with C. Therefore A, B, and C are incorrect choices for pairing with E in 16-bit operations.2

    Footnotes

    1. Registers of 8085 microprocessor - GeeksforGeeks - Overview of 8085 registers, including general-purpose registers and valid 16-bit pairings. ↩

    2. Intel 8085 - Wikipedia - Describes the 8085 as an 8-bit processor with 16-bit operations supported through register pairs BC, DE, and HL, plus SP. ↩

Common Exam Trap

Do not assume any two 8-bit registers can be joined into a 16-bit pair. In the 8085, the pairings are fixed as BC, DE, and HL only.

Footnotes

  1. Register Set of 8085 - PDF explaining that the only possible 8085 register pairs are BC, DE, and HL, and that they are used for 16-bit operations. ↩

Conceptual Deep Dive: Why DE Exists as a Pair

The 8085 is an 8-bit microprocessor, but it still needs to process 16-bit quantities such as addresses and larger data values. To support this efficiently, Intel defined three accessible 16-bit register pairs: BC, DE, and HL.2

Among these, HL is especially important because it is widely used as a memory pointer for indirect addressing.2 By contrast, BC and DE are commonly described as pairs used to hold 16-bit data. That architectural role further reinforces why E belongs with D and not with any other register.2

The logic is structural:

  • B pairs with C
  • D pairs with E
  • H pairs with L

This mapping is built into the instruction set and hardware interpretation of register-pair opcodes.2

Footnotes

  1. Intel 8085 - Wikipedia - Describes the 8085 as an 8-bit processor with 16-bit operations supported through register pairs BC, DE, and HL, plus SP. ↩ ↩2 ↩3 ↩4

  2. Register Set of 8085 - PDF explaining that the only possible 8085 register pairs are BC, DE, and HL, and that they are used for 16-bit operations. ↩ ↩2 ↩3 ↩4

  3. Registers in 8085: Definition, Types, Application & 16 Bit Registers - Testbook - Notes that register E is typically paired with D and lists BC, DE, and HL as valid pairs. ↩ ↩2

In the 8085, E combines with D to form the 16-bit register pair DE.2

Footnotes

  1. Register Set of 8085 - PDF explaining that the only possible 8085 register pairs are BC, DE, and HL, and that they are used for 16-bit operations. ↩

  2. Registers in 8085: Definition, Types, Application & 16 Bit Registers - Testbook - Notes that register E is typically paired with D and lists BC, DE, and HL as valid pairs. ↩

Valid 8085 Register Pair Membership

Each valid 16-bit pair contains exactly two fixed 8-bit registers.2

Footnotes

  1. Register Set of 8085 - PDF explaining that the only possible 8085 register pairs are BC, DE, and HL, and that they are used for 16-bit operations. ↩

  2. Registers in 8085: Definition, Types, Application & 16 Bit Registers - Testbook - Notes that register E is typically paired with D and lists BC, DE, and HL as valid pairs. ↩

Frequently Asked Clarifications

Final Examination-Oriented Conclusion

For the question:

For 16-bit operations, register E can be paired with what register?
(i) A
(ii) B
(iii) C
(iv) D

the correct choice is (iv) D because the valid 8085 register pairs are BC, DE, and HL, and therefore E pairs only with D in standard 16-bit register-pair operations.2

A compact memory aid is:

Valid pairs in 8085={BC, DE, HL}\text{Valid pairs in 8085} = \{BC,\ DE,\ HL\}

Since

E∈DEE \in DE

it follows that

E pairs with DE \text{ pairs with } D

This answer is both architecturally and instruction-set correct.2

Footnotes

  1. Register Set of 8085 - PDF explaining that the only possible 8085 register pairs are BC, DE, and HL, and that they are used for 16-bit operations. ↩ ↩2

  2. Registers in 8085: Definition, Types, Application & 16 Bit Registers - Testbook - Notes that register E is typically paired with D and lists BC, DE, and HL as valid pairs. ↩

  3. Intel 8085 - Wikipedia - Describes the 8085 as an 8-bit processor with 16-bit operations supported through register pairs BC, DE, and HL, plus SP. ↩

Knowledge Check

Question 1 of 4
Q1Single choice

In the 8085 microprocessor, register E forms a 16-bit pair with which register?

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