try to be more explanatory so that we can see what your problem. i dont like guess work since now i have to guess.
ok.The motor driver can use the same common ground but if you are using bread board try to check if your wires are connected firmly. as for the veroboard check that you have solder correctly then test. try to verify your connection. current i am using one h-bridge i have developed personally sharing the same GND with the micro controller.
actually now i am using the motor driver and the MCU in the PCB board that design by me
i have try the simualtion in the proteus software the coding can work. but after i work out with the circuit in the PCB i found out the voltage that given out from the port will drop to 0.++ after a few turn of the dc motor.
I not sure what is the problem on there. is that we can't use tamiya motor with the motor driver?
According to your schematic you have not used a series resistor on the LEDs connected to the CPU. That is a NO-NO. Use around 300 Ohm. Or calculate the series resistor with data from the LED data sheet