The board operates in the two modes:
1- RUN mode
2- PROGRAM mode
Run mode is a standard mode when AT89C51ED2 is running its own program.
Program mode is a special mode when the hardware conditions during the reset pulse forces the onchip
boot loader execution.
PC changes the board mode through the RS-232 serial interface by a using of RTS line.
PIC16F818 is polling this line permanently and if the signal changes the level then PIC16F818 switches
the board mode.