Reset Accumulator (8085 & 8086 microprocessor)
1. Problem – Write the 8085 instructions which reset the accumulator. Solution – There are 4 instructions to reset the accumulator in 8085. These instructions are:
|1||MVI A, 00||A <- 00|
|2||ANI 00||A AND 00|
|3||XRA A||A XOR A|
|4||SUB A||A <- A – A|
- MVI A, 00: instruction copies 00 to A.
- ANI 00: instruction performs bit by bit AND operation of source operand (i.e. 00) to the destination operand (i.e. the accumulator A) and store the result in accumulator A.
- XRA A: instruction performs XOR operation between source operand and destination operand and store the result in the accumulator. Here, source and destination operand both are same i.e. A. Therefore, the result after performing XOR operation, stored in the accumulator is 00.
- SUB A: operation subtracts the contents of source operand(here, source register is A) from the contents of accumulator and store the result in the accumulator itself. Since, the source and destination operand are same. Therefore, accumulator A = 00.
2. Problem – Write 8086 instructions which are used to reset accumulator. Solution – There are 4 instructions in 8086 to reset the accumulator. These instructions are:
|1||MOV AX, 0000||AX <- 0000|
|2||AND AX, 0000||AX <- AX AND 0000|
|3||XOR AX, AX||AX <- AX XOR AX|
|4||SUB AX, AX||AX <- AX – AX|
Explanation – Register AX is used.
- MOV AX, 0000: copies 0000 to AX.
- AND AX, 0000: operation performs bit by bit ANDs the source operand (0000) to the destination operand and store the result in AX.
- XOR AX, AX: performs the XOR operation in values of source register and destination register and store the result in AX. The source and destination operands, both are same. Therefore, AX = 0.
- SUB AX, AX: operation subtracts the value of source operand from the value of destination operand and store the result in AX. Here, both the operands are same .Therefore, AX = 0.
Initialization: The “Reset Accumulator” instruction is used to initialize the accumulator register to zero at the start of a program. This ensures that the accumulator is in a known state before any data processing operations are performed.
Error handling: The “Reset Accumulator” instruction can be used to handle errors in a program. If an error occurs during data processing, the accumulator can be reset to zero to prevent further errors and ensure that the program can continue executing properly.
Data processing: The “Reset Accumulator” instruction can be used in various data processing operations, such as arithmetic operations, logical operations, and data transfer operations. By resetting the accumulator to zero, the program can perform these operations on a fresh set of data.
Subroutine calls: The “Reset Accumulator” instruction can be used to clear the accumulator before calling a subroutine. This ensures that the subroutine operates on a clean set of data and does not interfere with the main program’s data processing operations.
Interrupt handling: The “Reset Accumulator” instruction can be used to clear the accumulator during interrupt handling. This ensures that the interrupt service routine operates on a clean set of data and does not interfere with the main program’s data processing operations.
Ensures accurate results: Resetting the accumulator before performing arithmetic or logical operations ensures that the results are accurate and do not include any previous data.
Improves efficiency: Resetting the accumulator can improve the efficiency of the program, as it eliminates the need to manually clear the accumulator each time a new operation is performed.
Reduces errors: Resetting the accumulator reduces the risk of errors due to leftover data from previous operations.
Slows down the program: Resetting the accumulator takes additional time, which can slow down the program execution.
Memory usage: Resetting the accumulator requires memory to store the instruction, which can be a disadvantage if memory usage is a concern.
May not be necessary: Resetting the accumulator may not be necessary in all cases, such as when the previous contents of the accumulator do not affect the current operation.
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