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📜  直接寻址模式和隐式寻址模式的区别

📅  最后修改于: 2021-09-27 14:56:08             🧑  作者: Mango

先决条件 – 寻址模式

1. 直接寻址方式:
在直接寻址模式下,地址字段包含操作数的地址。

Effective Address(EA) = address field of operand 

例子 –
将寄存器 A 的内容添加到累加器。

ADD A 

在地址 A 的内存中查找操作数。访问数据只需要一个内存引用。因此,不需要额外的计算来计算出有效地址。

2. 隐式寻址方式:
操作数在指令的定义中隐式指定。它通常用于零或单地址指令。

示例 1:
增加寄存器 A 的内容。

INC A 

这里隐式指定寄存器 A 既是源又是目标。

示例 2:
清除标志寄存器的内容。

CLC 

上面的指令是一个零地址指令的例子。

直接寻址模式和隐式寻址模式的区别:

DIRECT ADDRESSING MODE IMPLIED ADDRESSING MODE
Address fields contains the effective address of operand. Effective address of operand is specified implicitly.
Instruction size is larger since operand has to be explicitly specified. Instruction size is smaller since operand is specified implicitly.
It requires one reference to memory. No memory references are required.
Mostly used in 2 address instructions and more. Mostly used in zero address and single address instructions.
It is slower compared to implied mode. It is a faster method.
It has more range than implied mode. It has less range than direct mode.