Control mode of CPU

And CISC comparison ,RISC The advantages of ：
1） Better use VLSI The area of the chip ;
2） It can improve the operation speed ;
3） Easy to design , Can reduce costs , Improve reliability ;
4） It is conducive to compiler code optimization .
CPU Specific functions
1） Command control ： Complete the command , Analyzing and executing instructions , That is, the sequential execution of the program .
2） Operational control ：CPU Manage and generate the operation signal of each instruction fetched from memory , Send various operation signals to corresponding parts , In order to control these parts according to the command to carry out the action .
3） time control ： Time control of various operations .
4） The data processing ： Perform arithmetic and logical operations on data .
5） Interrupt handling ： Deal with abnormal situations and special requests during the operation of the computer .

How the controller works
According to the instruction opcode 、 The execution steps of the instruction （ Micro command sequence ） And condition signals to form the control signals to be used by various components of the current computer . The hardware system of the computer works together under the control of these control signals , Produce the expected results of execution .
1） The arithmetic unit is connected with the memory through the data bus 、 Input and output devices transmit data .
2） The input and output devices are connected with the bus through the interface circuit .
3） Memory 、 The I / O device receives address information from the address bus , Get the control signal from the control bus , Transfer data with other components through data bus .
4） The controller unit receives instruction information from the data bus , Receive instruction transfer address from arithmetic unit , Send instruction address to address bus , It also provides the components in the system with the control signals they need to operate .

Main functions of the controller
1） Take an instruction from main memory and indicate the location of the next instruction in main memory .
2） Decode or test instructions , Generate the corresponding operation control signal , In order to start the specified action .
3） Command and control CPU、 Main memory 、 The direction of data flow between input and output .

CPU Control mode of
1） Synchronous control mode
The system has a unified clock , All signals come from this unified clock signal .
The control circuit is simple , But it's slow .
2） Asynchronous control mode
There is no reference time scale signal , Each component works at its own inherent speed , Contact by answering .
Fast running speed , But the control circuit is more complex .
3） Joint control mode
Between synchronization 、 A compromise between asynchrony . Most of the micro operations of various instructions adopt synchronous control , A small part adopts asynchronous control .

Design steps of hardwired control unit ：
1） List the operation schedule of micro operation commands . Arrange according to the micro operation tempo , List the operation schedule of micro operation commands （ Including each machine cycle , Each instruction under the beat completes the operation control signal ）.
2） Carry out micro operation signal synthesis . Comprehensively analyze the micro operation signals 、 classified , According to the micromanipulation schedule, the logical expression of each micromanipulation control signal can be written and appropriately simplified .
3） Draw the logic diagram of micro operation command . According to the logic expression, the logic circuit diagram corresponding to each micro operation signal can be drawn , And realize with logic gate circuit .