thanks skimask. i solved the the underflow and overflow program. however, i got a new problem.

when i tested my program with rfpic12f675, and put probe at gp2 and gp5. the output is similar with what i simulated in mplab sim. there is preamble, header, and data bits. however, there is no change of output displayed on the oscilloscope even i dont supply any input to the transmitter. any suggestion why this happened?

the output always showed data bit of 1111 0111 which is weird since i sont supply any input to the system.

any suggestion anyone?