Why does the INC and DEC instructions not affect the carry flag?

By having INC / DEC set the Zero flag ( Z ), you could use them to control loops pretty nicely; by insisting the loop control instructions not change the Carry flag ( CF ), the carry is preserved across loop iterations and you can implement multiprecision operations without writing tons of code to remember the carry …

What is the difference between the carry flag and the overflow flag?

The carry flag is set if the addition of two numbers causes a carry out of the most significant (leftmost) bits added. If the sum of two numbers with the sign bits off yields a result number with the sign bit on, the “overflow” flag is turned on. 0100 + 0100 = 1000 (overflow flag is turned on) 2.

Does Inc set carry flag?

Incrementing it would produce Zero and hence ZF will be set to 1. (Do you still need CF?) in all the other cases carry flag will not be affected, so there is no need to produce duplicate indicator.So, keeping optimisation in mind, design of 8086 is made such that INC operation will not affect Carry flag.

What is the carry condition flag?

In computer processors the carry flag (usually indicated as the C flag) is a single bit in a system status register/flag register used to indicate when an arithmetic carry or borrow has been generated out of the most significant arithmetic logic unit (ALU) bit position.

Which flag is not effected by the INC and DEC instructions?

1. MOV or XCHG. No effect on flags. These are not arithmetic instructions.
2. INC and DEC. Sets all flags, except the CF. (I.e., CF is not affected by INC or DEC.)
3. ADD and SUB. Sets all flags.
4. NEG. Affects all flags with the following stipulations: CF = 1, unless result = 0. OF = 1, IF operand is 8000h or 80h.

Why carry flag is not affected by increment?

Why isn’t the carry flag affected in the increment operation of an 8085 microprocessor? – Quora. The INR Instruction preserves the Carry Flag so that it becomes easy for the user to implement counter like functionality into the code.

What’s the difference between overflow and carry?

The difference between Carry and Overflow is that Carry is used for unsigned numbers whereas Overflow is used for signed numbers. Carry is detected when addition of two numbers becomes a smaller number than the input terms.

What is the difference between auxiliary carry carry and overflow flag?

Generally carry is for unsigned, overflow is for signed, and auxiliary carry is an obscure thing not really used 🙂 But it’s indeed the carry from the low 4 bits to the high 4 bits.

How is overflow flag set?

The overflow flag is thus set when the most significant bit (here considered the sign bit) is changed by adding two numbers with the same sign (or subtracting two numbers with opposite signs). Internally, the overflow flag is usually generated by an exclusive or of the internal carry into and out of the sign bit.

What is carry and overflow?

Overflow indicates that a signed result is too big or too small to fit in the destination; Carry indicates that an unsigned result is too big to fit in the destination.

How do you get a carrying flag?

Carry Flag

1. The carry flag is set if the addition of two numbers causes a carry out of the most significant (leftmost) bits added. 1111 + 0001 = 0000 (carry flag is turned on)
2. The carry (borrow) flag is also set if the subtraction of two numbers requires a borrow into the most significant (leftmost) bits subtracted.

When auxiliary and carry flag will set to one if there is carry or else it is set to set?

This flag is used in BCD (Binary-coded Decimal) operations. The status of this flag is updated for every arithmetic or logical operation performed by ALU. This flag is set to one if there is a CARRY from the lower nibble or BORROW for the lower nibble in binary representation. Else it is set to zero.

What is the difference between carry flag and overflow flag in C?

From a mechanistic point of view, the carry flag is set when there is a carry out of the most-significant bit. The overflow flag is set when there is a carry into the most significant bit. With unsigned arithmetic you only have to worry about the carry flag.

When do you set the carry flag?

The Carry Flag is only set when an overflow occurs, but if I subtract any number from zero I don’t get an overflow. Or I am wrong? CF (bit 0) Carry flag — Set if an arithmetic operation generates a carry or a borrow out of the mostsignificant bit of the result; cleared otherwise.

What are the rules for turning on the overflow flag?

The rules for turning on the overflow flag in binary/integer math are two: If the sum of two numbers with the sign bits off yields a result number with the sign bit on, the “overflow” flag is turned on. If the sum of two numbers with the sign bits on yields a result number with the sign bit off, the “overflow” flag is turned on.

How does the carry flag affect the register size?

If the last step in which the two most significant bits generates a carry, then the carry flag is set. The carry flag will get added into the addition of the least significant bits of the next add. In affect, the carry flag increases the register size by 1 bit and become the most significant bit of the arithmetic operation.