DFRobot DFRduino Romeo-All in one Controller V1.1 Manual page 11

Sample Code：
//Standard DLL Speed control
int E1 = 4; //M1 Speed Control
int E2 = 7; //M2 Speed Control
int M1 = 5; //M1 Direction Control
int M2 = 6; //M1 Direction Control
///For previous Romeo, please use these pins.
//int E1 = 6;
//int E2 = 9;
//int M1 = 7;
//int M2 = 8;
//When m1p/m2p is 127, it stops the motor
//when m1p/m2p is 255, it gives the maximum speed for one direction
//When m1p/m2p is 0, it gives the maximum speed for reverse direction
void DriveMotorP(byte m1p, byte m2p)//Drive Motor Power Mode
Fig5: PLL Motor Control Pin Allocation Configuration
//M1 Speed Control
//M2 Speed Control
//M1 Direction Control
//M1 Direction Control