#define START_FRAME 0xABCD     	// [-] Start frme definition for reliable serial communication
#include <SoftwareSerial.h>
SoftwareSerial HSerial(2,3);        // RX, TX

typedef struct{
   uint16_t start;
   int16_t  steer;
   int16_t  speed;
   uint16_t checksum;
} SerialCommand;

SerialCommand Command;

void Send(int16_t uSteer, int16_t uSpeed)
{
  // Create command
  Command.start    = (uint16_t)START_FRAME;
  Command.steer    = (int16_t)uSteer;
  Command.speed    = (int16_t)uSpeed;
  Command.checksum = (uint16_t)(Command.start ^ Command.steer ^ Command.speed);
  // Write to Serial
  HSerial.write((uint8_t *) &Command, sizeof(Command)); 
}