Modbus Slave dengan Software Serial

#include <ModbusRTU.h>
#include <SoftwareSerial.h>
SoftwareSerial S(2, 3);
#define SLAVE_ID 4 //SILAHKAN DIGANTI ANGKANYA, SLAVE_ID 1 UNTUK HARDWARE SLAVE 1 dst.nya
ModbusRTU mb;
void setup() {
  Serial.begin(9600);
  S.begin(9600);
  mb.begin(&S);
  //mb.begin(&Serial, RXTX_PIN);  //or use RX/TX direction control pin (if required)
  mb.setBaudrate(9600);
  mb.slave(SLAVE_ID);
  pinMode(4, INPUT_PULLUP);
  pinMode(5, OUTPUT);
  pinMode(6, OUTPUT);
  mb.addCoil(0);  //tombol D4
  mb.addCoil(1);  //LED D5
  mb.addCoil(2);  //Buzzer D6
}
void loop() {
  mb.task();
  mb.Coil(0, digitalRead(4));
  digitalWrite(5, mb.Coil(1));
  digitalWrite(6, mb.Coil(2));
  delay(100);
}