1.通用寄存器:
8086CPU的所有寄存器都是16位, 可以存储2个字节. AX, BX, CX, DX 四个寄存器通常用来存放一般性的数据, 被称为通用寄存器.
8086CPU的上一代CPU中的寄存器都是8位的,为了保证兼容,8086CPU的 AX, BX, CX, DX 都可分为2个独立是使用的8位寄存器.
- AX --> AH & AL;
- BX --> BH & BL;
- CX --> CH & CL;
- DX --> DH & DL;
- ps: (H - High 高位, L - Low 低位)
2.16位结构的CPU, 有以下几方面的结构特性:
- 运算器一次最多可以处理16位的数据;
- 寄存器的最大宽度位16位;
- 寄存器和运算器之间的通路为16位;
3.8086CPU有20位地址总线, 可以传送20位地址,达到1MB的寻址能力, 8086又是16位结构, 在内部一次性处理, 传输, 暂时存储的地址为16位. 从8086CPU的内部结构来看, 如果将地址从内部简单地发出,那么它只能送出16位地址,表现出的寻址能力只有64KB.
8086CPU采用了一种在内部用两个16位地址合成的方法形成一个20位的物理地址.
- CPU中的相关不见提供2个16位的地址, 一个称为段地址, 一个称为偏移地址;
- 段地址和偏移地址通过内部总线送入一个称为地址加法器的部件;
- 地址加法器将这2个16位地址合成位一个20位的物理地址;
- 地址加法器通过内部总线将20位物理地址送入输入输出控制电路;
- 输入输出控制电路将20位物理地址送上地址总线;
- 20位物理地址被地址总线传送到存储器.
地址加法器采用 物理地址 = 段地址 * 16 + 偏移地址 的方法用段地址和偏移地址合成物理地址.
ps: 以二进制形式存放的段地址左移4位, 完成段地址 * 16的运算.
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