ATOM DTU modbus 写保持寄存器

#include <M5Atom.h>
#include <ArduinoModbus.h>
#include <ArduinoRS485.h>
#define RX_PIN      33
#define TX_PIN      23
uint16_t x = 1;
int i = 5;
RS485Class RS485(Serial2, RX_PIN, TX_PIN,-1,-1);
void setup() {
  M5.begin(true,true,true);
  if (!ModbusRTUClient.begin(9600, SERIAL_8E1)) {
        Serial.println("Failed to start Modbus RTU Client!");
        return;
  }
  delay(500);
}  
void loop() {
  if(!ModbusRTUClient.holdingRegisterWrite(7,1,x)){
    Serial.print("Failed to write holdingRegister! ");
    Serial.println(ModbusRTUClient.lastError());
  }
  x++;
  i--;
  if(i == 0){
    ModbusRTUClient.end();
    return;
  }
  delay(1000);
}