1.why timer2 in mod2 is used for serial communication? 2.why 11.0592MHz oscillator frequency is used for Mc-51?
"1.why timer2 in mod2 is used for serial communication?"
An 8051 microcontroller does not have a Timer-2; it is on the 8052 only.
See www.8052.com/tut8052.phtml for details.