Question

In 8085 microprocessor, which of the following are 2-byte instructions ?
• [A.] MOV C, A
• [B.] MVI A, 32H
• [C.] LDA 2050H
• [D.] JMP 2085H
• [E.] ADD B Choose the correct answer from the options given below :

• A. B and D Only
• B. B, D and E Only
• C. A, B and C Only
• D. B Only

Hint:

8085 instruction sizes: \[ \text{Opcode only} \Rightarrow 1 \text{ byte} \] \[ \text{Opcode + 8-bit data} \Rightarrow 2 \text{ bytes} \] \[ \text{Opcode + 16-bit address} \Rightarrow 3 \text{ bytes} \]

Answer 1

The Correct Option is D

Concept: 8085 instructions are classified as:
• 1-byte instructions
• 2-byte instructions
• 3-byte instructions Generally:
• Opcode only \(\rightarrow\) 1 byte
• Opcode + 8-bit data \(\rightarrow\) 2 bytes
• Opcode + 16-bit address \(\rightarrow\) 3 bytes

Step 1: Analyze instruction A. Instruction: \[ \texttt{MOV C,A} \] This transfers data between registers only. No immediate data or address is needed. Thus: \[ \texttt{MOV C,A} \] is a: \[ 1\text{-byte instruction} \] Therefore: \[ A \text{ is not correct} \]

Step 2: Analyze instruction B. Instruction: \[ \texttt{MVI A,32H} \] Here:
• First byte = opcode
• Second byte = immediate data \(32H\) Hence total size: \[ 2 \text{ bytes} \] Thus: \[ B \text{ is correct} \]

Step 3: Analyze instruction C. Instruction: \[ \texttt{LDA 2050H} \] This instruction requires:
• Opcode
• Lower-order address byte
• Higher-order address byte Thus: \[ 3 \text{ bytes} \] Hence: \[ C \text{ is not correct} \]

Step 4: Analyze instruction D. Instruction: \[ \texttt{JMP 2085H} \] This also needs:
• Opcode
• 16-bit address Thus: \[ 3 \text{ bytes} \] Therefore: \[ D \text{ is not correct} \]

Step 5: Analyze instruction E. Instruction: \[ \texttt{ADD B} \] This is register operation only. Thus: \[ 1 \text{ byte} \] Hence: \[ E \text{ is not correct} \]

Step 6: Determine the correct instruction. Only: \[ \texttt{MVI A,32H} \] is a 2-byte instruction.

Step 7: Write the final answer. Hence the correct option is: \[ \boxed{(D)\ B\ Only} \]