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GATE 2014 EC (EC4) – Question 52

Digital Circuits · Computer Organization · 2 marks · Multiple choice

An 8085 executes STA 1234H starting at address 1FFEH. STA copies the accumulator to the specified 16-bit address. During fetch and execution, what values appear sequentially at address pins A₁₅–A₈?

  1. 1FH, 1FH, 20H, 12H
  2. 1FH, FEH, 1FH, FFH, 12H
  3. 1FH, 1FH, 12H, 12H
  4. 1FH, 1FH, 12H, 20H, 12H

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Show answer and explanation

Correct answer: (A) 1FH, 1FH, 20H, 12H

Explanation

The three instruction bytes are fetched from1FFEH,1FFFH and2000H, whose high bytes are1FH,1FH and20H. The accumulator is then written to address1234H, presenting high byte12H. Thus the sequence is **1FH,1FH,20H,12H,A**. The16bit program counter crosses a page boundary during operand fetching.