Microcontroller--some basic classification

The predominant family of microcontrollers are 8-bit types since this word size has proved popular for the vast majority of tasks the devices have been required to perform. The single byte word is regarded as sufficient for most purposes and has the advantage of easily interfacing with the variety of IC memories and logic circuitry currently available. The serial ASCII data is also byte sized making data communications easily compatible with the microcontroller devices. Because the type of application for the microcontroller may vary enormously most manufacturers provide a family of devices, each member of the family capable of fitting neatly into the manufacturer’s requirements. This avoids the use of a common device for all applications where some elements of the device would not be used; such a device would be complex and hence expensive. The microcontroller family would have a common instruction subset but family members differ in the amount, and type, of memory, timer facility, port options, etc. possessed, thus producing cost-effective devices suitable- for particular manufacturing requirements.

Memory expansion is possible with chip RAM and/or ROM; for some family members there is no on-chip ROM, or the ROM is either electrically programmable ROM (EPROM) or electrically erasable PROM (EEPROM) known as flash EEPROM which allows for the program to be erased and rewritten many times. Additional on-chip facilities could include analog-to-digital conversion (ADC), digital-to-analog conversion (DAC) and analog comparators. Some family members include versions with lower pin count for more basic applications to minimize costs.