countdown timer code

I'm new to electronics and currently using Atmel 89c51 for my project.
Part of the project is a countdown timer with 4 units of 7segment display.
Once the timer reaches zero, it will trigger a dc motor.
Can some one provide me some idea on how to write the timer part?
Perheps can show me a sample code with only a digit of 7segment as a countdown timer for my reference...in addition, a button is added to increment the timer digit...
I referred to 8052.com and found a useful tutorial there providing me on how to trigger the motor once the timer reaches zero.
I'm stuck on the timer display part...

thanks