Memory Block Transfer Algorithm
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Questions and Answers

In the given algorithm for memory block transfer, what is the primary purpose of decrementing the D-E pair (destination pointer)?

  • To verify that the destination address remains within permissible memory bounds.
  • To prepare the destination pointer for the next block transfer operation elsewhere in memory.
  • To ensure the data is copied in reverse order, starting from the end of the destination block. (correct)
  • To free up the memory occupied by the transferred data in the source location.

If the counter C is initialized to 0AH (decimal 10), and the instruction at step 8 reduces C by one each loop, how many times will Step 4 be executed before the program halts?

  • 11
  • 0
  • 9
  • 10 (correct)

In the memory block transfer algorithm, what would happen if Step 7 (Decrement the destination pointer D-E pair) was accidentally replaced with 'Increment the destination pointer D-E pair'?

  • The program would halt prematurely due to an incorrect counter value.
  • The data transfer would still complete correctly, but at a slower pace.
  • The data would be written to the destination in reverse, overwriting itself and potentially other memory locations. (correct)
  • The data would be copied to the same memory location repeatedly, causing a system crash.

Given the algorithm, if the initial source memory location (H-L pair) is 2050H and the initial destination memory location (D-E pair) is 3060H, what will be the source and destination memory locations after the first byte is moved?

<p>Source: <code>2051H</code>, Destination: <code>305FH</code> (A)</p> Signup and view all the answers

Considering the provided algorithm, which of the following scenarios would most likely result in overwriting memory outside the intended destination block?

<p>Setting the initial destination memory location (D-E pair) to an address too close to the beginning of available memory and using a large counter value. (C)</p> Signup and view all the answers

In the provided 8085 assembly code, what is the primary purpose of Register D?

<p>To store the carry generated during addition. (C)</p> Signup and view all the answers

Consider the instruction JNC LOOP1. What condition must be true for the program to jump to LOOP1?

<p>The carry flag must not be set. (A)</p> Signup and view all the answers

What is the purpose of the INX H instruction in the given code snippet?

<p>To increment the HL register pair to point to the next memory location. (C)</p> Signup and view all the answers

If the first number loaded into Register B is 0x7F and the second number loaded into Register C is 0x02, how many times will the INR D instruction be executed?

<p>1 (B)</p> Signup and view all the answers

After the execution of the instruction LXI H, 2100H, what does the HL register pair contain?

<p>The address 2100H. (C)</p> Signup and view all the answers

What will be the final value stored in the accumulator after the execution of the provided code if the number at memory location 2100H is 05H and the number at 2101H is 03H?

<p>00H (C)</p> Signup and view all the answers

Which instruction in the given code directly affects the value of the Carry flag?

<p>ADD B (C)</p> Signup and view all the answers

What would happen if the JNZ LOOP2 instruction was replaced with JMP LOOP2?

<p>The program would enter an infinite loop. (D)</p> Signup and view all the answers

In the given 8085 assembly code, what is the primary purpose of the JNC LOOP instruction at memory address 200A?

<p>To jump to the <code>LOOP</code> label only if the addition operation did not result in a carry. (D)</p> Signup and view all the answers

Based on the provided code and the given input values (2100=FF, 2101=05), what value will be stored in memory location 2200 after executing the program?

<p>04 (C)</p> Signup and view all the answers

What is the role of Register C in this 8085 assembly program?

<p>To store the carry generated during the addition of the two numbers. (D)</p> Signup and view all the answers

If the instruction at 2009 was changed from ADD B to SUB B, how would it affect the value stored in memory location 2200?

<p>2200 would store the difference of the two numbers. (D)</p> Signup and view all the answers

What would be the effect of removing the INR C instruction at memory address 200D?

<p>The carry would never be stored, resulting in an incorrect final carry value. (C)</p> Signup and view all the answers

Suppose the instruction at 200A is changed to JC LOOP. How would this single change alter the program's execution flow?

<p>The program will jump to the LOOP label only when there is a carry. (D)</p> Signup and view all the answers

In the provided assembly code snippet, what is the purpose of the STA 2200H instruction?

<p>To store the contents of the accumulator into memory location 2200H. (B)</p> Signup and view all the answers

In the given assembly code, which instruction is responsible for storing the carry flag's value in a memory location?

<p><code>MOV A,C</code> and <code>STA 2201</code> (A)</p> Signup and view all the answers

If the values at memory locations 2100 and 2101 were both changed to 01H, what would be the values stored at 2200 and 2201 after execution?

<p>2200 = 02, 2201 = 00 (C)</p> Signup and view all the answers

What is the purpose of MOV A,D instruction?

<p>Move the contents of register D into the accumulator (D)</p> Signup and view all the answers

According to the provided algorithm for finding the absolute difference between two numbers, what happens if a carry is generated during the comparison of the two numbers?

<p>The two numbers are swapped before subtraction. (A)</p> Signup and view all the answers

In the absolute difference algorithm, why is it necessary to compare the two numbers before subtracting?

<p>To ensure that the result is always positive by subtracting the smaller number from the larger number. (D)</p> Signup and view all the answers

What is the function of the HLT instruction?

<p>It halts the execution of the program. (A)</p> Signup and view all the answers

In the provided code, what is the significance of the memory addresses 2100 and 2101 in relation to the absolute difference calculation?

<p>They store the two input numbers for which the absolute difference will be calculated. (C)</p> Signup and view all the answers

Why does the algorithm initialize the H-L pair to the source memory location in Step 1?

<p>To point to the memory locations from where the two numbers to be compared are loaded. (C)</p> Signup and view all the answers

How does the provided flowchart indicate that the absolute difference between two numbers is being calculated, rather than just the difference?

<p>By including a step to check for a carry and swap the numbers if necessary, ensuring the subtraction always yields a positive result. (D)</p> Signup and view all the answers

In the provided algorithm, what is the primary purpose of initializing the DE register pair to a memory location one byte less than the actual destination (3500H)?

<p>To ensure the data is written to the correct destination address by incrementing it before the first write operation. (B)</p> Signup and view all the answers

If the counter C is initialized with the value 05H, how many times will the loop between Step 4 and Step 11 of the algorithm be executed?

<p>5 times (C)</p> Signup and view all the answers

What would be the effect of omitting Step 4 ('Increment HL pair and DE pair') from the algorithm?

<p>Only the first byte of data would be transferred repeatedly, overwriting the same memory locations. (B)</p> Signup and view all the answers

In the provided program snippet LXI H, 2500, what does the instruction LXI H do?

<p>Initializes the HL register pair with the immediate 16-bit address 2500H. (C)</p> Signup and view all the answers

Suppose the carry flag is set during the execution of this program. How will this affect the overall functionality of the memory transfer process?

<p>The carry flag has no impact on this memory transfer process, as it is not used in any conditional jump instructions. (D)</p> Signup and view all the answers

What is the purpose of initializing register B to 00 at the beginning of the program?

<p>To count the number of occurrences of a specific data value (DB) within the block. (C)</p> Signup and view all the answers

What is the significance of the instruction LXI H,205FH in the given program?

<p>It initializes the HL register pair with the address 205F, pointing to the start of the data block's length. (D)</p> Signup and view all the answers

What would be the value stored in memory location 2100H after the program execution, given the provided input data?

<p>02 (B)</p> Signup and view all the answers

What is the purpose of the CMP M instruction in the loop?

<p>To compare the content of memory location pointed by HL register with accumulator A. (B)</p> Signup and view all the answers

If the JNZ instruction at address 200AH was replaced with JZ 200EH, how would the program's behavior change?

<p>The program would count non-<code>DB</code> values instead. (D)</p> Signup and view all the answers

What happens when the DCR C instruction is executed and the value in register C becomes zero?

<p>The zero flag is set, and the program continues to the next instruction. (C)</p> Signup and view all the answers

Suppose the memory location 205F contained the value 00. What would be the final value stored in 2100H and why?

<p>00, because the loop will not execute. (C)</p> Signup and view all the answers

If the instruction INX H was accidentally skipped (removed) from the loop, how would this impact the program's functionality?

<p>The program would get stuck in an infinite loop, repeatedly comparing the same memory location. (A)</p> Signup and view all the answers

Flashcards

LDA Instruction

Loads the content of a memory location into the accumulator.

ADD Instruction

Adds the content of a specified register to the accumulator.

JNC Instruction

Jumps to a specified address if the carry flag is not set.

INR Instruction

Increments the content of a specified register by one.

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STA Instruction

Stores the content of the accumulator into a memory location.

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MOV Instruction

Moves data from one register to another.

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HLT Instruction

Halts program execution.

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Accumulator

A temporary storage location in the CPU used for arithmetic and logical operations.

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Initialize Counter

Sets up a register (C) to act as a loop counter, determining how many bytes will be copied.

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Source Pointer (HL)

Points to the memory location from where data will be copied.

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Destination Pointer (DE)

Points to the memory location where data will be stored.

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Move Byte to Accumulator

Moves a byte from the source memory location into the accumulator for processing.

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Move Byte to Destination

Moves a byte from the accumulator to the destination memory location.

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MOV A,D

MOV A, D moves the content of register D into the accumulator (register A).

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Absolute Difference

An instruction to find the magnitude of the difference between two numbers.

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H-L Register Pair

The H-L register pair is often used as a memory pointer to indirectly access memory locations.

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CMP Instruction

The CMP (Compare) instruction compares the content of the accumulator with the content of a specified register or memory location.

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Carry Flag in Comparison

Carry flag helps determine which number is larger.

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Swapping Numbers

Modifies instructions when the initial comparison reveals that the numbers were not in the order required for direct subtraction

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What is the purpose of Reg.D?

Reg.D is initialized to 00H to store the carry generated during addition.

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Why initialize the accumulator to 00H?

The accumulator is initialized to 00H to ensure a clean starting point for summing the numbers.

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What is loaded into Reg. B?

The first number to be added is loaded from memory into register B.

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What is loaded into Reg. C?

The second number, dictating loop iterations, is loaded into register C.

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What does ADD B do?

The 'ADD B' instruction adds the content of register B to the accumulator. The result is stored in the accumulator.

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What does JNC do?

JNC (Jump if No Carry) is a conditional jump instruction. If, after the addition, no carry flag is set, the program jumps to the specified address.

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What does INR D do?

INR D increments the content of register D by 1. It's used to count the number of carry operations.

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What does DCR C do?

DCR C decrements the content of register C by 1. It is used to control the loop, indicating how many times the addition should be performed.

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LXI H, memory address

Points HL to the memory location where the counter is stored.

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Counter Register C

Sets up register C to control the number of loop iterations.

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LXI D, memory address

Points DE to a designated memory area, typically for storing or manipulating data.

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Increment HL / DE pair

Increments the memory address pointed to by HL or DE to access the next memory location.

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Decrement C

Reduces the value in register C by one, used to control loop repetitions.

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Start

The starting point of the program.

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MVI B, 00

Set the B register to zero. This is used to count occurrences.

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LXI H, 205FH

Load HL register pair with the address 205FH. HL points to the start of the data block.

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MOV C, M

Move the contents of memory pointed to by HL into the C register. C now stores the block length.

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MVI A, DB

Move the immediate data (DB) into the accumulator (A).

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INX H

Increment the HL register pair, moving the pointer to the next memory location.

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CMP M

Compare the content of memory pointed by HL with the content of the accumulator A.

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HLT

Halt: stops program execution.

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Study Notes

  • This is a collection of practical programming exercises for an 8085 microprocessor.
  • The exercises cover fundamental operations such as addition, subtraction, multiplication, data transfer, and logical operations.
  • Each practical exercise details the aim, algorithm, flowchart, program code, and expected results.

Practical No. 1: Addition of Two 8-Bit Numbers

  • Accumulator and Register B contain the two numbers to be added
  • Register C stores the carry
  • The sum is stored in the accumulator, and the carry is stored in Register A.

Practical No. 2: Addition of Two 16-Bit Numbers

  • HL register stores the first 16 bit number
  • The sum of the lower bytes is stored in memory location 2200.
  • The carry is stored in memory location 2201.
  • The DE register pair temporarily holds the first 16-bit number.

Practical No. 3: Subtraction of Two 8-Bit Numbers

  • The accumulator is used along with register B to preform the subtraction of the two 8-bit numbers
  • If a carry is generated, it indicates that the result is negative.
  • The difference is stored in the accumulator and any carry is stored in register A.

Practical No. 4: Multiplication of Two 8-Bit Numbers

  • Registers B and C hold the two numbers to be multiplied.
  • Register D stores the carry.
  • The program repeatedly adds the contents of register B to the accumulator
  • It loops until register C becomes zero.
  • The final result is stored in memory location 2200 and the carry in 2201.

Practical No. 5: Finding Absolute Difference Between Two Numbers

  • The absolute difference between two 8-bit numbers is calculated.
  • The two input numbers are compared.
  • The smaller one is subtracted from the larger one to determine the difference.

Practical No. 6: Adding Contents of Memory Blocks

  • Contents of two blocks of memory are added together and stored into the third block of memory
  • HL pair, BC pair, and DE pair are used as source and destination pointers

Practical No. 7: Transferring Data in Reverse Order

  • The blocks of data stored in memory locations 2100h to 2109h.
  • Data is transferred in reverse order to memory locations starting from 3100h.

Practical No. 8: Exchanging Contents of Two Blocks

  • The program exchanges the contents of two blocks of memory.
  • The size of the block is stored in memory location 2500h.

Practical No. 9: Counting Occurrences of a Number

  • A program is written to count how many times number DB occurs in the data.
  • The result is stored in memory location 2100.
  • Initializing the HL pair to 205F.

Practical No. 10: Finding Odd and Even Numbers

  • This program finds odd and even numbers in a block of data from memory locations from 2501h.
  • This program stores the size of the block in memory location 2500h.

Practical No. 11: Dividing Two Numbers

  • 1 byte Hex number is divided, where the dividend is stored in 2030H and the division is stored in 2031H.
  • Quotient and remainder are stored in the next consecutive memory location respectively.

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Description

This lesson explores a memory block transfer algorithm, focusing on pointer manipulation and loop control. It covers decrementing the destination pointer, loop execution count, and the consequences of incorrect pointer updates. It also looks at memory locations after transfer.

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