What is the purpose of control flag?
(b) Control Flags – The control flags enable or disable certain operations of the microprocessor. There are 3 control flags in 8086 microprocessor and these are: Directional Flag (D) – This flag is specifically used in string instructions.
What are the uses of flag in microprocessor?
Flags are a modified kind of register that record the condition of a microprocessor’s calculation. For instance, a “zero status” flag is activated only when the microprocessor’s calculation concludes with a “zero” status.
What is the purpose of the status register?
The status register lets an instruction take action contingent on the outcome of a previous instruction. Typically, flags in the status register are modified as effects of arithmetic and bit manipulation operations.
What are the commonly used condition code flags?
2. The Processor Flags (Condition Codes)
- Processor status is described as condition codes, or status flags.
- Condition codes refer to the information about most recently executed instruction.
- For example, if decrementing a register produces zero value, the zero flag ZF is set by the processor.
What register determines the status of the flag register?
The FLAGS register is the status register in Intel x86 microprocessors that contains the current state of the processor. This register is 16 bits wide. Its successors, the EFLAGS and RFLAGS registers, are 32 bits and 64 bits wide, respectively. The wider registers retain compatibility with their smaller predecessors.
What is the job of the CPU’s flag register?
Processor Status and Flags Register. Individual bits in the FLAGS register give information about the status of the processor. Status flags – reflect the results of computations (add, subtract, multiply, divided) executed by the processor.
Which flag bit of status register is affected by BST instruction?
A bit from a register in the register file can be copied into T by the BST instruction, and a bit in T can be copied into a bit in a register in the register file by the BLD instruction. The half carry flag H indicates a half carry in some arithmetic operations.
How do you use a flag register?
In 8085 microprocessor, flag register consists of 8 bits and only 5 of them are useful. The 5 flags are: Sign Flag (S) – After any operation if the MSB (B(7)) of the result is 1, it indicates the number is negative and the sign flag becomes set, i.e. 1.
What register determines the status of the flag register explain with examples?
The FLAGS register is one example of a status register which was used in certain central processor units and contained current states of a processor. It was 16 bits wide and was succeeded by EFLAGS and RFLAGS, a 32-bit register and 64-bit register, respectively.
Which flag is affected by SBB instruction?
The SBB instruction does not distinguish between signed or unsigned operands. Instead, the processor evaluates the result for both data types and sets the OF and CF flags to indicate a borrow in the signed or unsigned result, respectively. The SF flag indicates the sign of the signed result.
Which group of instructions do not affect the flag?
As there is no arithmetic or logical operation being performed, no flags are affected by data transfer instructions. Arithmetic Instructions are the instructions that perform basic arithmetic operations such as addition, subtraction, and a few more.
Which of the following instruction will affects the flag?
only carry and zero flags will be affected. no flags will be affected. While STC instruction executes, microprocessor sets the carry flag to 1. So this instruction affects the carry flag only.
What kind of a flag is the sign flag?
8. What kind of a flag is the sign flag? Explanation: Sign flag is a type of status register or the flag register. It is used to indicate the sign of certain bits.
How do you change the direction of a flag?
Set Direction Flag (std)
- Operation. 1 -> DF.
- Description. Sets the direction flag to 1, causing all subsequent string operations to decrement the index registers, (E)SI and/or (E)DI, used during the operation.
- Example. Set the direction flag: std.