Microcontroller

Microcontroller

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  By Mahalakshmi Embedded Engineer1
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  What is Microcontroller? Microcontrolleris a single chip self-contained computer single chip devices or single chip computers.  A programmable single chip which controls a process or system. Integrated circuit with pins along each side. Microcontrollers are used in appliances, automobile, scientific instrument etc.., 2
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  Difference between Microcontroller andMicroprocessor A microcontroller is not the same as a microprocessor. A microprocessor is a single chip CPU used within other computer systems. A microcontroller is itself a single chip computer system. 3
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  Components  A microcontrollerhas seven main components: Central processing unit (CPU)  ROM  RAM  Input and Output  Timer  Interrupt circuitry  Buses 4
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  Architecture  There aretwo basic types of architecture:  Harvard Von Neumann.  Microcontrollers most often use a Harvard or a modified Harvard-based architecture. 5
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  Von Neumann Von Neumannarchitecture has a single, common memory space where both program instructions and data are stored. There is a single data bus which fetches both instructions and data. The advantage to this architecture lies in its simplicity and economy. 6
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  Harvard Architecture Harvard architecturecomputers have separate memory areas for program instructions and data. There are two or more internal data buses which allow simultaneous access to both instructions and data. This speeds up execution time at the cost of more hardware complexity. 7
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  The Central ProcessingUnit  The central processing unit (CPU) does all the computing.  It fetches, decodes and executes program instructions and directs the flow of data to and from memory.  The CPU performs the calculations required by program instructions and places the results of these calculations, if required, into memory space. 8
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  CPU Components CPU Contains Registers ALU AddressBus Data bus 9
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  Contd..,  Arithmetic logicunit, or ALU: One part of the CPU is responsible for performing calculations and executing instructions. ALU contains the decoder, the sequencer and a variety of registers. Decoder: It converts instructions stored in program memory into codes which the ALU can understand. Sequencer: It manages the flow of data along the microcontroller’s data bus. Registers: It temporarily store vital data which are volatile: they can change during program execution. 10
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  Registers The stack pointer:The stack pointer contains the address of the next location on the stack. The address in the stack pointer is decremented when data is pushed on the stack and incremented when data is popped from the stack.  The index register: The index register is used to specify an address when certain addressing modes are used. 11
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  Contd.., The program counter:The PC holds the address of the next instruction in program memory space. It contains the address of the next instruction the CPU will process. As each instruction is fetched and processed by the ALU, the CPU increments the PC. The accumulator: The accumulator is a register that can hold operands or results of operations as necessary. The Microchip devices use the name W (working) register. 12
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  ROM  ROM, readonly memory, is non-volatile memory used for program information and permanent data.  The microcontroller uses ROM memory space to store program instructions it will execute when it is started or reset. 13
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  RAM RAM, random accessmemory, is used to write and read data values as a program runs. RAM is volatile: if you remove the power supply its contents are lost. Any variables used in a program are allocated from RAM. 14
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  I/O Ports There aretwo main port types, parallel and serial, and two port modes,synchronous and asynchronous. Parallel I/O requires a data line for each bit,while serial I/O uses a single line and transfers bits in sequence. Synchronous I/O is synchronised to a clock while asynchronous I/O is not. 15
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  Timer A timer isa counter that is incremented at a fixed rate when the system clock pulses.  A timer/counter can perform several different tasks. The CPU uses the timer to keep track of time accurately. The timer can generate a stream of pulses or a single pulse at different frequencies. It can be used to start and stop tasks at desired times. 16
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  Interrupt Circuitry An interruptis an event that suspends regular program operation while the event is serviced by another program. Interrupts increase the response speed to external events. When an interrupt is received current operation is suspended, the interrupt is identified and the controller jumps (vectors) to an interrupt service routine. There are two sources of interrupt: hardware and software. Hardware interrupts include a signal to a pin, timer overflow, and serial port interrupts. Software interrupts are commands given by the programmer, 17
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  Thank You 18