先决条件 – 硬连线 v/s 微程序控制单元
为了执行指令，有两种类型的控制单元：硬连线控制单元和微程序控制单元。
- 硬连线控制单元通常比微程序设计更快。在硬连线控制中，我们看到了如何使用状态计数器和 PLA 电路生成 CPU 内部所需的所有控制信号。
- 微程序控制单元是一种相对简单的逻辑电路，能够(1)对微指令进行排序和(2)产生控制信号以执行每个微指令。
| Hardwired Control Unit | Microprogrammed Control Unit |
|---|---|
| Hardwired control unit generates the control signals needed for the processor using logic circuits | Micrprogrammed control unit generates the control signals with the help of micro instructions stored in control memory |
| Hardwired control unit is faster when compared to microprogrammed control unit as the required control signals are generated with the help of hardwares | This is slower than the other as micro instructions are used for generating signals here |
| Difficult to modify as the control signals that need to be generated are hard wired | Easy to modify as the modification need to be done only at the instruction level |
| More costlier as everything has to be realized in terms of logic gates | Less costlier than hardwired control as only micro instructions are used for generating control signals |
| It cannot handle complex instructions as the circuit design for it becomes complex | It can handle complex instructions |
| Only limited number of instructions are used due to the hardware implementation | Control signals for many instructions can be generated |
| Used in computer that makes use of Reduced Instruction Set Computers(RISC) | Used in computer that makes use of Complex Instruction Set Computers(CISC) |