Timer plays the most useful and important part in Embedded System Design. Timers are useful to generate delays, reading the scheduled data, and for many more applications. The timer is the hardware part of microcontroller. A timer is basically a counter driven by external clock or internal clock of microcontroller. Timers can be of 8-bit or 16-bit wide. The configuration of timer and size of timer depend on the architecture and vendor of microcontroller. Timer is an interrupt based device, generates an interrupt on completion of configured time. Every microcontroller has different Interrupt Service Vector Address.