Flags in 8086 microprocessor pdf

The 8086p operate in the real mode memory addressing. In 8086 there are 6 different flags which are set or reset after 8bit or 16bit operations. What are the different types of flags in a 8086 microprocessor. The operands are either the registers or memory locations immediate data depending upon the addressing mode. Flag register in 8085 microprocessor geeksforgeeks. Eu execution unit execution unit gives instructions to biu stating from where to fetch the data and then decode and execute those instructions. Carry flag cy, auxiliary carry flag ac, sign flag s, parity flag p, and. The arithmetic instructions affect all the conditional code flags. The flag bits affected by the add instructions are. Figure below shows the details of the 16 bit flag register of 8086 cpu. Unit2 8086 assembly language programming ece department microprocessors and microcontrollers page 5 to this type of instructions. Intel 64 and ia32 architectures software developers manual pdf. Where seven bits remain unused or it is rest and remain nine bits are used. Set if the signed result cannot be expressed within the number of bits in the destination operand.

There are 3 control flags in 8086 microprocessor and these are. This register has 9 flags which are divided into two parts that are as follows. For example the zero flag zf will set if the result of execution of an instruction is zero. There is one flag registers which contain number of flags what is a flag. When set flag termed as set is in position 1 and in 0 position it is termed as reset. In 8085 microprocessor, flag register consists of 8 bits and only 5 of them are useful. The flag bits are changed to 0 or 1 depending upon the value of result after arithmetic or logical operations. Here the microprocessor is interrupted after every instruction so that the program can be debugged. It indicates some condition produced by the execution of an instruction. The respective position of these flag bits in flag register has been show the below figure. Thus a flag can be represented by 1 bit of information. Interrupt enable flag ifit is used to mask disable or unmask enable the intr interrupt.

The 8086 microprocessor has a 16 bit register for flag register. Conditional flags represent result of last arithmetic or logical instruction executed. Sign flag s after any operation if the msb b7 of the result is 1, it indicates the number is negative and the sign flag becomes set, i. An interrupt that can be turned off by the programmer is known as maskable interrupt. Microprocessor 8086 functional units tutorialspoint. Directional flag d this flag is specifically used in string instructions. If interrupt flag is set 1, the microprocessor will recognize. Which microprocessor accepts the program written for 8086 without any changes. Real mode operation allows the microprocessor to address only the first 1 mbyte of memory. The flags register it is a 16bit register, also called program status. Flag register of 8086 microprocessor tutorialspoint. In 8086 carry flag, parity flag, auxiliary carry flag, zero flag, overflow flag, trace flag, interrupt flag, direction flag, and sign flag. Execution unit receives program instruction codes and data from biu, executes these instructions and store the result in general registers.

Flag register of 8086 microprocessor geeksforgeeks. As shown in the below figure, the 8086 cpu is divided into two independent functional parts o bus interface unitbiu o execution uniteu dividing the work between these two units speeds up processing. Flag registers intel 80868088 microprocessor conditional flags. Flag register is a 16bit register, but there are only 9 flags available in the 8086 microprocessor. In 8085 microprocessor, the flags register can have a total of eight flags.