TMR0 interrupt for 16F84A

I want to use TMR0 interrupt. I use PIC Basic Pro 2.42A with MicroCode Studio 2.3 to write and compile my programs. I want to wait my PIC from PC's serial data. If no data is received after 1 or 2 seconds and I want to do other work. Why can I write these codes in PICBasic Pro.

Thanks

you have to enable the (over flow interrupt of TMR0),,