#include "ModbusRtu.h"
#define ID   1      // адрес ведомого

//Задаём ведомому адрес, последовательный порт, выход управления TX
Modbus slave(ID, 0, 0);

constexpr uint8_t all_registers_count = 29;
uint16_t all_registers[all_registers_count]{};
#define TIME_L 5

// write
  // service: [0, 1]
  // controls: [lining, right/left lifting]
  // indicators: [...]
// read
  // sensors


// write[<=12]
  // service: [0, 1]
  // controls: [2, 3, 4]
  // indicators: [5, 6, 7, 8, 9, 10]
// read[>12]
  // sensors [12, 13, 14, ..., 28]






// service: 0, 1
// write
// read
int i = 0;

void setup() {
  // настраиваем последовательный порт ведомого
  slave.begin(115200);
}

void loop() {
  static unsigned long prev_time{};
  unsigned long cur_time = millis();
  if (cur_time - prev_time > TIME_L) {
    i++;
    prev_time = cur_time;
  }
  if (prev_time > cur_time) prev_time = cur_time;
  int8_t state = slave.poll(all_registers, all_registers_count);
  io_poll();
}

void io_poll() {
  const uint16_t register_number_data = all_registers[0];//holding
  all_registers[1] = register_number_data * 2;//input
  const bool register_flag_data = all_registers[2];//coil
  all_registers[3] = !register_flag_data;//discrete input
}