8086 cpu标志积存器

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于 2006-01-23 18:17:00 发布

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本文详细介绍了CPU中的各种标志位及其作用：CarryFlag(CF)指示无符号溢出；ZeroFlag(ZF)在结果为零时设置；SignFlag(SF)反映结果正负；OverflowFlag(OF)指示有符号溢出；ParityFlag(PF)与结果中1的数量有关；AuxiliaryFlag(AF)用于低四位的无符号溢出；InterruptenableFlag(IF)控制外部中断响应；DirectionFlag(DF)决定数据处理方向。

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Carry Flag (CF) - this flag is set to 1 when there is an unsigned overflow. For example when you add bytes 255 + 1 (result is not in range 0...255). When there is no overflow this flag is set to 0.
Zero Flag (ZF) - set to 1 when result is zero. For none zero result this flag is set to 0.
Sign Flag (SF) - set to 1 when result is negative. When result is positive it is set to 0. Actually this flag take the value of the most significant bit.
Overflow Flag (OF) - set to 1 when there is a signed overflow. For example, when you add bytes 100 + 50 (result is not in range -128...127).
Parity Flag (PF) - this flag is set to 1 when there is even number of one bits in result, and to 0 when there is odd number of one bits. Even if result is a word only 8 low bits are analyzed!
Auxiliary Flag (AF) - set to 1 when there is an unsigned overflow for low nibble (4 bits).
Interrupt enable Flag (IF) - when this flag is set to 1 CPU reacts to interrupts from external devices.
Direction Flag (DF) - this flag is used by some instructions to process data chains, when this flag is set to 0 - the processing is done forward, when this flag is set to 1 the processing is done backward.