FLAG REGISTERS IE1 YASHhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh.pptx

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1. Intel ® 80386 Microprocessor: FLAG REGISTER Name- Yash A. Dongare IE-1: Presentation DIV-B PRN:122B1B077

2. Intel ® 80386 Microprocessor Registers are  a type of computer memory built directly into the processor or CPU (Central Processing Unit) that is used to store and manipulate data during the execution of instructions . A register may hold: 1)Computer instructions 2)Storage address 3)Or any kind of data 2

3. Intel ® 80386 Microprocessor: Flag Register 3 Flag Register of 80386 : The Flag register of 80386 is a 32 bit register. Out of the 32 bits, Intel has reserved bits D18 to D31, D5 and D3, while D1 is always set at 1.Two extra new flags are added to the 80286 flag to derive the flag register of 80386. They are VM and RF flags.

4. Intel ® 80386 Microprocessor: Flag s C F (Carry Flag ) –It holds the carry after calculations. P F (Parity Flag ) –Parity is a logic for odd parity and a logic 1 for even parity. Parity is a count of ones in a number expressed as even or odd. A C (Auxiliary carry) –Carry occurs bits positions 3 and 5 of the results. Z F (Zero Flag ) – The zero flag shows that the result of an arithmetic or logical operation is zero. When Z = 1, the result is zero. When Z = 0, the result was non-zero. 4

5. S F( Sign) – The sign flag holds the arithmetic sign after an arithmetic or a logical operation. If S =1 the sign bit is set and the result is negative. If S = 0, the sign bit is not set and the result is positive. I F (Interrupt Flag ) – The interrupt flag controls the operations of the INTR(Interrupt request) input pint. If I =1, the INTR pin is enabled; if I =0, the INTR pin is disabled. VM (virtual mode) – If this flag set, the 80386 enters the virtual mode within the protected mode. In this mode, if any privileged instruction is executed, an exception 13 is generated. 5 T F (Trap Flag ) – Enables trapping through an on-chip debugging facility.

6. 6 9. RF (R esume Flag ) – The resume flag is used with debugging to control the resumption of execution after the next instruction. 10. NT ( N ested task Flag ) – The nested task flag is used to indicate that the current task is nested within another task in protected mode operation. This flag is set when the task nested by software. 11. IOPL (I/O Privilege level) – IOPL is used in protected mode operation to select the privilege level for I/O devices. IF the current privilege level is higher or more trusted than the IOPL, I/O executed without hindrance. If the IOPL is lower than the current privilege level, an interrupt occurs.

7. VM - Virtual Mode Flag : If this flag is set, the 80386 enters the virtual 8086 mode within the protection mode. This is to be set only when the 80386 is in protected mode. In this mode, if any privileged instruction is executed an exception 13 is generated. This bit can be set using IRET instruction or any task switch operation only in the protected mode. RF- Resume Flag : This flag is used with the debug register breakpoints. It is checked at the starting of every instruction cycle and if it is set, any debug fault is ignored during the instruction cycle. The RF is automatically reset after successful execution of every instruction, except for IRET and POPF instructions. 7

8. References Flag registers of 80386 microprocessor- geeks for geeks. Systems Flags-MIT Registers-of-80386-microprocessor 18

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