CASE STUDY OF MICRO-PROGRAMMED CONTROL UNIT AND HARDWIRED CONTROL UNIT
Guided by :- Dr. S.T Patil
Department of Computer Science. Vishwakarma Institute of Technology, Pune, 411037, Maharashtra, India.
Introduction
Any computer in any facility has a crucially important device i.e. the CPU or the central processing unit. It is often referred to as the “Brain of the computer”, implying that a computer can’t do anything without it. It is the fundamental processing unit that provides the instructions and processing power to the computer to perform a specific task.The CPU has two main systems, one is the arithmetic logic unit(ALU) and the other is the control unit(CU). ALU handles all the arithmetic and logical operations whereas the CU synchronizes the tasks by sending timings and control signals. A control unit can be either micro-programmed or hardwired. This case study aims to study these two types.
A control unit (CU) handles all the processor control signals. It directs all enter and output flow, fetches code for commands from microprograms, and directs different gadgets and fashions with the aid of presenting manage and timing signals. A CU thing is taken into consideration by the processor mind as it troubles orders to pretty much the whole thing and guarantees accurate training execution. A CU takes its center from the training and standing registers. Its regulations of operation, or microprogram, are encoded in a programmable good judgment array (PLA), random good judgment, or read-simplest reminiscence(ROM). CUs are designed in ways: hardwired i.e. layout is primarily based totally on a hard and fast structure and microprogrammed i.e. microprograms are saved in a unique manage reminiscence and are primarily based totally on flowcharts.
Micro-programmed Control Unit:-
The concept of microprogramming was added via means of Maurice Wilkies in 1951 as an intermediate degree to execute pc application instructions. A programming technique is used to put into effect a micro-programmed manipulation unit. An application together with microinstructions is used to carry out a chain of micro-operations. Each bit of bureaucracy the microinstruction is related to at least one manipulate sign. When the bit is set, the manipulate sign is active. When it’s miles cleared the manipulate sign turns inactive. These microinstructions in a series may be stored withinside the internal ‘manipulate’ memory.
Characteristics:
- The microinstruction cope with is precise withinside the manipulate reminiscence cope with sign up.
- All the manipulated statistics is stored withinside the manipulated reminiscence(ROM).
- The microinstruction acquired from reminiscence is saved withinside the manipulate sign up.
- A manipulate phrase withinside the microinstruction specifies one or more than one micro-operations for a records processor.
- The subsequent cope with is calculated withinside the circuit of the following cope with generator/ the microprogram sequencer after which transferred to the manipulate cope with sign up for analyzing the following microinstruction whilst the micro-operations are being executed.
Working:
Step 1: The instruction to execute is fetched and stored in the instruction register.
Step 2: The microinstruction cope with generator element fetches the coaching from the coaching sign in and decodes the coaching.
Step 3: On interpreting the instruction, the microinstruction cope with generator generates the beginning cope with the corresponding micro routine in the control store.
Step 4: The microinstruction copes with generator masses the beginning of the microprogram ordinary into the Microprogram counter. This permits the microinstruction to deal with generators to track the addresses of successive microinstructions of the habitual.
Step 5: The microinstruction cope with generator increments the microprogram counter to examine the successive training withinside the micro habitual gift withinside the manage store.
Step 6: The quit of the micro habitual may be decided with the assist of a chunk withinside the closing training of the micro habitual. This bit is called the quit bit. When the quit bit is same to one it defines a hit execution of the micro habitual. This causes the brand new training to be fetched.
Advantages:
- It allows for a more methodical control unit design.
- It is less complicated to debug and change.
- The implementation of a microprogram managed unit is much less costly.
- It is used to do complex functions with ease.
- It is more flexible and adaptable.
Disadvantages:
- Adaptability is obtained at more cost.
- It is slower than a hardwired managed unit.
Hardwired Control Unit:-
Hardwired control units are implemented through the use of combinational logic units, featuring a finite number of gates that can generate specific results based on the instructions used to invoke those responses. It is constructed by physically connecting components such as gates, flip-flops, and drums, hence the hardwired controller name.
Characteristics:
- 2 decoders, a sequence counter, and logic gates make up a hardwired control.
- Memory unit (IR) instructions are stored in the instruction register.
- The instruction register consists of the operation code.
- A 3 X 8 decoder is used to encode the operation bits 12 through 14.
- The decoder’s outputs are denoted by ‘D0’ through ‘D7’.
- Flip-flop with the symbol ‘I’ is used to transfer bit 15 operation code.
- From bits 0 to 11, operation codes are programmed into the control logic gates.
- The sequence counter can count from 0 to 15 in binary.
Methods for designing the hardwired control logic:
- Sequence Counter Method — It is the most practical and convenient way to design a moderately complex controller.
- Delay Element Method — It depends on the timed delay elements to create the sequence of the control signals.
- State Table Method — It involves the traditional algorithmic approach in designing the notes controller utilizing the classical state table method.
Working:
The basic data for control signal creation is contained in the operation code of instruction. Instruction decoders decode operation codes.There are a number of fields in the instruction opcode that can be decoded using the instruction decoder.As a result, only a few output lines of the command decoder have active signal values. These output lines are coupled to the inputs of the matrix and provide control signals to the computer’s execution units. This matrix combines the decoded signal of the instruction opcode with the output of this matrix. B. Interrupt signal. Matrices are constructed in the same manner as programmable logic arrays.
Advantages:
- It is quick due to the usage of combinational circuits in fact faster than a microprogrammed CU.
- The quantity of put off that could arise withinside the advent of manipulate indicators is depending on the range of gates.
- It may be tweaked to get the quickest mode of operation.
Disadvantages:
- The design becomes more complex if additional control signals are to be created.
- It is difficult and time-consuming to either add a new feature or change an existing feature.
- It is complicated to evaluate and fix flaws in the design.
- It can be a little bit expensive.
Hardwired vs Microprogrammed:
Speed
In the hardwired control unit, the speed of operations is very fast. In contrast, the micro-programmed manage unit desires common reminiscence access. So the rate of operation of a microprogrammed manipulate unit is slow.
Modification
Modifications to the Hardwired control unit mean redesigning the entire unit whereas, in the micro-programmed control unit, modification can be done by changing the microinstructions in the control memory. Hence, the micro-programmed control unit is more flexible.
Cost
The implementation of a Hardwired control unit is very much compared to the Micro-programmed control unit.
Handling Complex Instructions
Complex instructions can get difficult to handle when using a hardwired control unit unlike the micro-programmed control unit as it makes them easy to handle.
Instruction Decoding
Again, it is difficult to decode instructions using a hardwired control unit. Using a micro-programmed control unit can make the task easy.
Instruction Set Size
A hardwired control unit uses a small instruction set whereas a micro-programmed control unit uses a large instruction set.
Control Memory
The hardwired control unit does not use the control memory to generate the control signals, but the microprogrammed CU needs to use the control memory to generate the control signals.
Applications
The hardwired control unit is used in those types of processors that basically use RISC. On the other hand, a micro-programmed control unit is used in those types of processors that basically use CISC.
Conclusion
In conclusion, we can say that the Hardwired control unit is a type of sequential circuit used to generate the control signals. In contrast, the micro-programmed control unit is a type of unit used to contain the microinstruction in the control memory so that it can generate the control signals. This is the main difference between both control units. Apart from this difference both the control units have their own advantages and disadvantages over one another but both are widely used in various applications.
References
- Sebestian, Amity University https://www.coursehero.com/file/p2ukadq/case-study-Q1-Give-the-organization-of-Micro-programmed-control-unit-and-explain/\
- William Mason High School, https://www.coursehero.com/file/82985348/CASE-STUDY-MICRO-PROGRAMMED-VERSUS-HARDWIRED-CONTROL-UNITS-HOW-COMPUTERS-REALLY-WORKpdf/
- UKEssays. (November 2018). Micro Programmed Control And Hardwired Control Information Technology Essay. Retrieved from https://www.ukessays.com/essays/information-technology/micro-programmed-control-and-hardwired-control-information-technology-essay.php?vref=1
- Microprogrammed Control, https://www.pvpsiddhartha.ac.in/dep_it/lecturenotes/CSA/unit-3.pdf
Publishers:
Arpit Vidhale, Shivani Vikhar, Akash Waghmare, WAGH ISHITA
Department of Computer Science and Engineering.
Vishwakarma Institute of Technology, Pune, 411037, Maharashtra, India
