I'm currently working on a project related to solar trackers. I have developed functions which are based on time in which the tracker will move. I'm only familiar with the "MC9S12DT256B" microcontroller as thats the board I've used during my studies at school. My question is: How can a microcontroller tell time? I know there are timers, but I've also read stuff about external clock sources and "Real Time Clock with Embedded Crystal". Which series of microcontroller should I be looking into? Are they attachable onto such microcontrollers? Any suggestions would be appreciated. Thank you.