The system circuit of the whole MSP430F149 microcontroller is to connect the crystal oscillator circuit module, reset circuit module, keyboard circuit module, dc motor driver circuit with MSP430F149 microcontroller, and then the microcontroller's Vcc connection +5V power supply, Vss grounding, as shown in figure 4.1.This design realizes the control of the motor through four keys. The keys are connected to port P2, and the keys are pressed to change the level. The changed level is sent to port P0.0 and P0.1 through the single chip microcomputer. It is also generated in the PWM pulse to the enable end of L298N, so as to control the speed of the motor.