Thanks for the reply,
I have tested by sending '0' to receiver when no button is pressed. This works but it keeps busy tx, rx all the time even when the car is standing. In addition one strange thing also starts that when i want to reverse the car, there is some delay now i.e. the car will continue forward motion for a fraction of second before it decides to go reverse. The spring button on tx sending '1' in forward has to pass through center (sending 0) and then to other side to send '2' for reverse. May be passing from 1-----0-----2 is too fast to handle by tx and rx, i cant say anything.
This is the reason i want rx to understand that when no button is pressed, keep the car in stop condition. This is the same situation when i first turn on tx and rx, car is motionless as tx is not sending anything. How i can do this by code?