Control Unit Operation
... A single micro-operation generally involves a transfer between registers, a transfer between a register and an external bus, or a simple ALU operation. ... • The control unit of a processor performs two tasks: o It causes the processor to execute micro-operations in the proper sequence, determined by the program being executed, and o it generates the control signals that cause each micro-operation to be executed • The control signals generated by the control unit cause the opening and closing of logic gates, resulting in the transfer of data to and from registers and the operation of the ALU. • One technique for implementing a control unit is referred to as hardwired implementation, in which the control unit is a combinatorial circuit. Its input logic signals, governed by the current machine instruction, are transferred into a set of output control signals. MICRO-OPERATIONS Operation of a computer in executing a program consists of a sequence of instruction cycles, with one machine instruction per cycle. ... CONTROL OF THE PROCESSOR Functional Requirements The functional requirements for the control unit are those functions that the control unit must perform. A definition of these functional requirements is the basis for the design and implementation of the control unit. With the information at hand the following three-step process leads to a characterization of the control unit: 1. ... Determine the functions that the control unit must perform to cause the micro operations to be performed. The basic functional units of a processor are: • ALU • Registers • Internal data paths • External data paths • Control unit Some thought should convince you that this is a complete list.