The selection of microcontroller depends upon the type of application. The following factors must be considered while selecting the microcontroller.
1. Word length: The word length of microcontroller is either 8, 16 or 32 bit. As the word length increases, the cost, power dissipation and speed of the microcontroller increases.
2. Power dissipation: It depends upon various factors like clock frequency, speed, supply voltage, VLSI technology etc. For battery operated embedded systems, we must use low power microcontrollers.
3. Clock frequency: The speed of an embedded system depends upon the clock frequency. The clock frequency depends upon the application.
4. Instruction Set: On the basis of instructions microcontrollers are classified into two categories 1. CISC 2. RISC. CISC system improves software flexibility. Hence it is used in general purpose systems. RISC improves speed of the system for the particular applications.
5. Internal resources: The internal resources are ROM, RAM, EEPROM, FLASH ROM, UART, TIMER, watch dog timer, PWM, ADC, DAC, network interface, wireless interface etc. It depends upon the application for which microcontroller is going to be used.
6. I/O capabilities: The number of I/O ports, size and characteristics of each I/O port, speed of operation of the I/O port, serial port or parallel ports. These are the considerations needed to ascertain.
7.Memory: For mass production of microcontrollers ROM versions and for lesser production EPROM version or CPU version with external program memory is suitable