Largest element in an array | 8085 Lab Program

 Section: Array Operations & Code Conversions

Aim: To find the largest element in an array of data stored in memory and also to verify the result.

Apparatus Required: 8085 microprocessor kit, keyboard.

Algorithm:

1. Place all the elements of an array in consecutive memory locations.
2. Fetch the first element from the memory location and load it in the accumulator.
3. Initialize a counter (register) with the total number of elements in an array (or total comparisons \(n-1\)).
4. Decrement the counter by 1.
5. Increment the memory pointer to point to the next element.
6. Compare the accumulator content with the memory content (next element).
7. If the accumulator content is smaller, then move the memory content (largest element) to the accumulator; else continue.
8. Decrement the counter by 1.
9. Repeat steps 5 to 8 until the counter reaches zero.
10. Store the result (accumulator content) in the specified memory location.

Program:

Address	Label	Mnemonics	Operand	Comment
4100		LXI	H, 4200	Initialize HL reg. to data location
4103		MVI	B, 04	Initialize B reg with no. of comparisons (\(n-1\))
4105		MOV	A, M	Transfer first data to accumulator
4106	LOOP1	INX	H	Increment HL reg. to point next memory location
4107		CMP	M	Compare M & A
4108		JNC	LOOP	If A is greater than M then go to loop
410B		MOV	A, M	Transfer data from M to A reg
410C	LOOP	DCR	B	Decrement B reg
410D		JNZ	LOOP1	If B is not Zero go to loop1
4110		STA	4205	Store the result in a memory location
4113		HLT		Stop the program

Observation:

• Input:
  • 4200: 01
  • 4201: 06
  • 4202: 03
  • 4203: 07
  • 4204: 02
• Output:
  • 4205: 07

Result: Thus the largest number in the given array is found and it is stored at location 4205.

Flowchart:

               +-------------------+
               |       START       |
               +---------+---------+
                         |
                         v
               +-------------------+
               |   [HL] <- 4200H   |
               +---------+---------+
                         |
                         v
               +-------------------+
               |     [B] <- 04H    |
               +---------+---------+
                         |
                         v
               +-------------------+
               |    [A] <- [M]     |
               +---------+---------+
                         |
                         v <------------------+
               +-------------------+          |
               |  [HL] <- [HL] + 1 |          |
               +---------+---------+          |
                         |                    |
                         v                    |
                       /     \                  |
                     /  Is     \                |
                   / [A] < [HL]? \            |
                  <   (CY = 1)    >           |
                   \             /            |
                     \         /              |
                       \     /                |
                        \   /                 |
            +-----------+--+                  |
            |              |                  |
           YES             NO                 |
            |              |                  |
            v              |                  |
  +-------------------+    |                  |
  |    [A] <- [HL]    |    |                  |
  +---------+---------+    |                  |
            |              |                  |
            +-------+------+                  |
                    |                         |
                    v                         |
          +-------------------+               |
          |   [B] <- [B] - 1  |               |
          +---------+---------+               |
                    |                         |
                    v                         |
                  /   \                       |
                /  Is   \                     |
              /   [B] = 0? \                  |
             <              >                 |
              \  Is Zero?  / -- NO -----------+
                \        /
                  \    /
                    | YES
                    v
          +-------------------+
          |     <- [A]  |
          +---------+---------+
                    |
                    v
          +-------------------+
          |       STOP        |
          +-------------------+

Viva Questions:

1. What is meant by the instruction CMP M?
2. What the instruction JNZ will do?
3. State the logic behind the finding of largest element.
4. List out the similarities b/w the CALL-RET and PUSH-POP instructions?
5. What is the need of ALE signal in 8085?
6. What are the addressing modes of 8085?

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