Microcontrollers generally can be classified into 8-bit, 16-bit, and 32-bit family based on the size of their arithmetic and index register(s). It generally consists of ROM(Read Only Memory), RAM(Random Access Memory), Stack Pointers, Registers, Accumulator, Input/Output Ports, Timers, Analog to Digital Converter(ADC), Digital to Analog Converter(DAC), UART or SPI (for communication purposes).
Some have special built in features that comes with Liquid Crystal Display Driver (LCD) that will enable them to drive LCD displays, EEPROM (Electrical Eraseable Programmable Read Only Memory) which is a non volatile memory that will enable it to store data permanently.
It can be implemented using high level language or assembly language. Clock speed determines how much processing can be accomplished in a given amount of time by the MCU.
Some have a narrow clock speed range. Sometimes a specific clock frequency is chosen to generate another clock required in the system, e.g. for serial baud rates. Generally the higher clock frequencies, the higher the system costs because not only does the it cost more, but so do all the support chips required, such as RAMs, ROMs and bus drivers.
The processing technology of the microcontroller are N-channel metal oxide semiconductor (NMOS) or high-density complementary metal-oxide semiconductor (HCMOS).
In HCMOS, signals drive from rail-to-rail, unlike earlier NMOS processors. Since these criteria can significantly affect noise issues in system design, HCMOS uses less power and thus generates less heat.
The design geometries in HCMOS are smaller, which permit denser designs for a given size and thus allow higher bus speeds. The denser designs also allow lower cost, for more units can be processed on the same sized silicon wafer. For these reasons, most MCUs today are produced using HCMOS technology.
Advantages of Microcontroller compared to Microprocessor
The advantages of microcontroller are that all MCUs have on-chip resources to achieve a higher level of integration and reliability at a lower cost. An on-chip resource is a block of circuitry built into the MCU which performs some useful function under control of the MCU.
Built-in resources increase reliability because they do not require any external circuitry to be working for the resource to function. They are pre-tested by the manufacturer and conserve board space by integrating the circuitry into the MCU.
Some of the more popular on-chip resources are memory devices, timers, system clock/oscillator, and I/O. Memory devices include read/write memory (RAM), read-only memory (ROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), and electrically erasable memory (EEM). The term EEM actually refers to an engineering development version of an MCU where EEPROM is substituted for the ROM to reduce development time.
Timers include both real-time clocks and periodic interrupt timers. Other timer functions include timer compare and/or input capture lines.
I/O includes serial communication ports, parallel ports (I/O lines), analog to digital (A/D) converters, digital-to-analog (D/A) converters, liquid crystal display drivers (LCD), and vacuum fluorescent display drivers (VFD).
Other built-in resources may include computer operating properly (COP) watchdog system which can be hardware or software based.
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