Flag Registers

    One last important register is the flags register. These registers control how certain instruction work, such as the conditional jumps (in BASIC, they are like IF-THEN's). They are stored as bits (0's or 1's) in the flags register. We will most often use:

• zero => ZR/NZ (zero/not zero) - tells you whether an instruction (such as subtraction):
• yielded a zero as an answer sign => NG/PL (negative/positive), tells you whether an instruction
• yielded a positive or negative number carry => CY/NC (carry/no carry) - tells you whether an instruction needed to carry a bit (like in addition, you carry a number over to the next digit). Various system (BIOS) functions use this flag to denote an error.
• direction => DN/UP (decrement/increment) - tells a block instruction to either move forward or backwards in reads and writes.