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The status register is a set of flag bits within a processor used for programming purposes. Each flag has a unique purpose, such as the carry, zero, disable interrupt, decimal, overflow, and negative flags. The FLAGS register was replaced by EFLAGS and RFLAGS.
The status register, also known as the flag register, program status word, and condition code register, is defined as a set of flag bits within a processor. A register is a processor circuit and is very similar to a memory location, meaning that data can be written to and read from it. Unlike a memory location, the state register often doesn’t have an address because the microprocessor uses it internally. In a central processing unit (CPU) which is 8-bit, a status register bit can be set, equal to the number 1, or cleared, equal to the number 0, from assorted processor operation results. The processor sometimes sets or clears the bits itself, but other times, a particular program instruction sets or clears the bits.
Status register bits are also called flags or flag bits and are used by the programmer for certain programming purposes. Each flag in a state register has a unique purpose. The carry flag sets whether a previous operation overflowed the seventh bit, or negative flag, or overflowed the carry flag. Set during the rounds of logic, comparison and arithmetic. The zero flag is set if the result of the most recent operation was 0.
A flag called “disable interrupt” operates by allowing or disallowing the operation of interrupts, which are instructions that temporarily halt certain operations so that other operations can be performed. When this particular flag is set, interrupts cannot operate, but when it is clear, interrupts are allowed. Another flag called the decimal flag allows the processor to follow a more advanced binary mode to perform flawless arithmetic equations. When the flag is set, use this enhanced binary mode. Another bit in the register is the interrupt flag bit, which is set when the Force Interrupt (BRK) command is executed.
An overflow flag is set during arithmetic operations if an operation produces an invalid result. The negative flag is set if the result of the most recent operation had set it to 1. A final flag, called bit 5, is unnamed and always set to 1. Programmers essentially have no need for this particular bit.
The FLAGS register is an example of a status register which was used in some central processing units and held the current states of a processor. It was 16 bits wide and has been replaced by EFLAGS and RFLAGS, a 32-bit register and a 64-bit register, respectively. The FLAGS register, however, had a few different flags from the original 8-bit register, including the parity flag, auxiliary flag, and trap flag.
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