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In the 8086/8088, the overflow flag is set when the result of an arithmetic instruction exceeds the bounds of the signed representation of a number. This is not the same as the carry flag, which is used for the unsigned representation. Both flags get set as needed. You decide which one to pay attention to.
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What is the usage of 8086 status register?
The 8086 status register, also known as the FLAGS register, is crucial for controlling the operation of the microprocessor. It contains individual flags that reflect the status of the processor and the outcome of arithmetic and logical operations, including the Zero Flag, Sign Flag, Overflow Flag, and Carry Flag. These flags are used for conditional branching and to indicate conditions such as equality, overflow, and carry-out, influencing program flow and decision-making processes within applications.
Explain 8086 flag register?
FLAGS REGISTER="h2headingh3"style="color:rgb(0,0,0);"name="flags_register">Flags Register - determines the current state of the processor. They are modified automatically by CPU after mathematical operations and allow one to determine the type of the result as well as determine conditions to transfer control to other parts of the program. Generally you cannot access these registers directly.Carry Flag (CF) - this flag is set to 1 when there is an unsigned overflow. For example when you add bytes 255 + 1 (result is not in range 0...255). When there is no overflow this flag is set to 0.Parity Flag (PF) - this flag is set to 1 when there is even number of one bits in result, and to 0 when there is odd number of one bits.Auxiliary Flag (AF) - set to 1 when there is an unsigned overflow for low nibble (4 bits).Zero Flag (ZF) - set to 1 when result is zero. For non-zero result this flag is set to 0.Sign Flag (SF) - set to 1 when result is negative. When result is positive it is set to 0. (This flag takes the value of the most significant bit.)Trap Flag (TF) - Used for on-chip debugging.Interrupt enable Flag (IF) - when this flag is set to 1 CPU reacts to interrupts from external devices.Direction Flag (DF) - this flag is used by some instructions to process data chains, when this flag is set to 0 - the processing is done forward, when this flag is set to 1 the processing is done backward.Overflow Flag (OF) - set to 1 when there is a signed overflow. For example, when you add bytes 100 + 50 (result is not in range -128...127).
Difference between carry flag and overflow flag in 8086?
The carry flag indicates that an arithmetic operation between two numbers resulted in an unsigned carry or borrow. The overflow flag indicates that an arithmetic operation between two numbers resulted in an unexpected change in sign, i.e. an overflow. Carry is also like overflow. The difference is in interpretation. Do you consider the numbers signed or unsigned? Its all in interpretation because the hardware logic needed to add two numbers works the same, no matter if they are considered signed or unsigned. Both flags are set or cleared together, so you can use whichever you wish.
How is parity flag affected with the or instruction in 8086 microprocessor?
In the 8086 microprocessor, the parity flag (PF) is affected by the OR instruction based on the result of the operation. The parity flag is set if the number of set bits (1s) in the result is even; it is cleared if the number of set bits is odd. Therefore, after executing an OR instruction, the parity flag reflects the parity of the result of the logical OR operation performed on the operands.
What are the flags affected after add instruction execution?
After the execution of an ADD instruction, the following flags in the processor's status register may be affected: the Zero Flag (ZF), which is set if the result is zero; the Sign Flag (SF), which indicates if the result is negative; the Carry Flag (CF), which is set if there is an overflow from the most significant bit; and the Overflow Flag (OF), which is set if the addition results in an overflow for signed integers. Additionally, the Parity Flag (PF) may also be updated based on the parity of the result.
What type of flags in 8086 and 8088 microprocessor and their uses.?
There are nine flags in the 8086/8088.SF - Sign Flag - The result is negativeZF - Zero Flag - The result is zeroAF - Auxillary Carry Flag - A BCD carry occurredPF - Parity Flag - Indicates the oddness or evenness of the number of bitsCF - Carry Flag - An unsigned carry occurredOF - Overflow Flag - A signed overflow/carry occurredDF - Direction Flag - Controls the direction of repeated string operationsIF - Interrupt Flag - Enables or disables interruptsTF - Trace Flag - Controls the debug single step interruptIn general, most of these flags are set as a result of some arithmetic or logical instruction and can be tested using the conditional branch instructions. Exceptions are DF, which controls the directionality of repeated string operations, IF, which controls interrupts, and TF, which controls debugging.
what type of flags in 8086 and 8088 microprocessor and their uses?
There are nine flags in the 8086/8088.SF - Sign Flag - The result is negativeZF - Zero Flag - The result is zeroAF - Auxillary Carry Flag - A BCD carry occurredPF - Parity Flag - Indicates the oddness or evenness of the number of bitsCF - Carry Flag - An unsigned carry occurredOF - Overflow Flag - A signed overflow/carry occurredDF - Direction Flag - Controls the direction of repeated string operationsIF - Interrupt Flag - Enables or disables interruptsTF - Trace Flag - Controls the debug single step interruptIn general, most of these flags are set as a result of some arithmetic or logical instruction and can be tested using the conditional branch instructions. Exceptions are DF, which controls the directionality of repeated string operations, IF, which controls interrupts, and TF, which controls debugging.
What is meant by flag is set or not set in 8085 processor?
The flags are testable conditions that are set after many arithmetic or logical instructions to indicate something about the result of the result. For instance, the Z flag means the result is zero, the N flag means it is negative, the O flag means a signed overflow occurred, the C flag means an unsigned overflow occurred, and the P flag means an even number of bits is set in the result. You can use the various flag testable jump instructions, such as JZ or JNZ to test the flag after performing an operation that sets or resets the flag.
Which flags are affected after ADD instruction?
After an ADD instruction, the flags affected typically include the Zero Flag (ZF), which is set if the result is zero; the Sign Flag (SF), which indicates the sign of the result; the Carry Flag (CF), which is set if there is a carry out of the most significant bit; and the Overflow Flag (OF), which is set if there is an overflow in signed arithmetic. Additionally, the Parity Flag (PF) may also be affected, depending on the result's parity.
Enlist the types of flags in 8086?
The 8086 microprocessor has several types of flags, categorized into two main groups: status flags and control flags. Status flags include the Zero Flag (ZF), Sign Flag (SF), Parity Flag (PF), Carry Flag (CF), and Overflow Flag (OF), which indicate the outcome of arithmetic and logical operations. Control flags include the Direction Flag (DF), which determines the direction of string operations, and the Interrupt Flag (IF), which enables or disables interrupts. Additionally, there is a Trap Flag (TF) used for single-step debugging.
When two numbers multiply what happens to the O and C flag bits?
When two numbers multiply, the Overflow (O) and Carry (C) flag bits are affected based on the result of the multiplication. The Overflow flag is set if the result exceeds the maximum representable value for the given data type, indicating a signed overflow. The Carry flag is typically set if there is a carry out from the most significant bit, which occurs in unsigned multiplication when the result exceeds the capacity of the destination register. Thus, both flags indicate potential issues with the result's representation.
Condition flags available in 8086?
Conditional FlagsConditional flags represent result of last arithmetic or logical instruction executed. Conditional flags are as follows:1. CF (Carry Flag)This flag indicates an overflow condition for unsigned integer arithmetic. It is also used in multiple-precision arithmetic.2. AF (Auxiliary Flag)If an operation performed in ALU generates a carry/barrow from lower nibble (i.e. D0 - D3) to upper nibble (i.e. D4 - D7), the AF flag is set i.e. carry given by D3 bit to D4 is AF flag. This is not a general-purpose flag; it is used internally by the processor to perform Binary to BCD conversion.3. PF (Parity Flag)This flag is used to indicate the parity of result. If lower order 8-bits of the result contains even number of 1's, the Parity Flag is set and for odd number of 1's, the Parity Flag is reset.4. ZF (Zero Flag)It is set; if the result of arithmetic or logical operation is zero else it is reset.5. SF (Sign Flag)6. SF (Sign Flag)In sign magnitude format the sign of number is indicated by MSB bit. If the result of operation is negative, sign flag is set.7. OF (Overflow Flag)This stands for over flow flag. It occurs when signed numbers are added or subtracted. An OF indicates that the result has exceeded the capacity of machine. It becomes set if the sign result cannot express within the number of bites.Read More: http://www.daenotes.com/electronics/digital-electronics/8086-8088-microprocessor
