отсюда https://groups.google.com/forum/#!msg/VladRusanov/yZXoytGlqgc/PlqpCmqDFAAJ
Приложение 4.

#include <SoftwareSerial.h>
//-------- порты для rs 485
#define SSerialRx        11  // Serial Receive pin RO
#define SSerialTx        8   // Serial Transmit pin DI
//-------- инициализация 
SoftwareSerial RS485Serial(SSerialRx, SSerialTx); // Rx, Tx

//// линия управления передачи приема
#define SerialControl 5   // RS485 Direction control
/////// флаг приема передачи
#define RS485Transmit    HIGH
#define RS485Receive     LOW
/////// команды
byte testConnect[] = { 0x00, 0x00 };
byte Access[]      = { 0x00, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01};
byte Sn[]          = { 0x00, 0x08, 0x00 }; // серийный номер
byte Freq[]        = { 0x00, 0x08, 0x16, 0x40 }; // частота
byte Current[]     = { 0x00, 0x08, 0x16, 0x21 };//  ток
byte Suply[]       = { 0x00, 0x08, 0x16, 0x11 }; // напряжение
byte Power[]       = { 0x00, 0x08, 0x16, 0x00 };// мощность
byte Angle[]       = { 0x00, 0x08, 0x16, 0x51 }; // углы
byte activPower[]  = { 0x00, 0x05, 0x00, 0x00 };///  суммарная энергия прямая + обратная + активная + реактивная
byte sumPower[]    = { 0x00, 0x08, 0x11, 0x00 };
byte response[19];
int byteReceived;
int byteSend;
int netAdr;
int SCAN_YES_NO=0;
int TST_YES_NO=0;  
int ACCESS_YES_NO=0;
int ALLOW=0; 

void setup() {
RS485Serial.begin(9600);
Serial.begin(9600);
// 5 пин в режим выхода
pinMode(SerialControl, OUTPUT);
// ставим на прием
digitalWrite(SerialControl, RS485Receive);
delay(300);
Serial.println("Start_v02.01\r\n");
}

void loop() {

TST_YES_NO=0;  
ACCESS_YES_NO=0;
ALLOW=0;  
                      
               while (Serial.available()) 
              {    char incomingBytes[15]; 
              
                   if(Serial.available()>0)       
                    {      
                        Serial.readBytes(incomingBytes,10);
                     
                    }                   
                           String getS = String(incomingBytes);
                               if(getS.substring(0,5) == "init_") 
                            { ALLOW=1;  
                                   Serial.print(getS.substring(0,5)+getS.substring(5,8)+"\r\n");
                              netAdr=getS.substring(5,8).toInt();
                            }


                               if(getS.substring(0,5) == "loop_") 
                            { ALLOW=1;
                              SCAN_YES_NO=1;  
                              Serial.print(getS.substring(0,5)+getS.substring(5,8)+"\r\n");
                              netAdr=getS.substring(5,8).toInt();
                            }

                                  if(getS.substring(0,5) == "stop_") 
                            { ALLOW=0;
                              SCAN_YES_NO=0;  
                              Serial.print(getS.substring(0,5)+"000\r\n");
                              //netAdr=getS.substring(5,8).toInt();
                            }

                                  if(getS.substring(0,5) == "ping_") 
                            {   
                              Serial.print(getS.substring(0,5)+"\r\n");
                              
                            }
                      
            
                }
 



 if(ALLOW==1 or SCAN_YES_NO==1)
{
 //========================================================================
  testConnect[0] = netAdr;
  response[0] = 0;
  send(testConnect, sizeof(testConnect), response);
       if(response[0] == netAdr)
      {      TST_YES_NO=1;
             Serial.print("Connect_OK\r\n");   
              
             
      }
       else
      {      TST_YES_NO=0;
             Serial.print("Connect_FAIL\r\n");   
      }


  //========================================================================

     if(TST_YES_NO==1)
     {
          
          delay(100);
          Access[0] = netAdr;
          response[0] = 0;
          send(Access, sizeof(Access), response);
              if(response[0] == netAdr)
             {      ACCESS_YES_NO=1;
                    Serial.print("Access_OK\r\n");   
             }
              else
             {      ACCESS_YES_NO=0;
                    Serial.print("Access_FAIL\r\n");   
             }

     }

        if(ACCESS_YES_NO==1)
     {

         String serNum = getSerialNumber(netAdr);
         Serial.print("s:"+ serNum +"\r\n");   
         String ARPower = getARPower(netAdr);
         Serial.print("p:"+ ARPower+"\r\n");   
         String valFreq = getFreq(netAdr);
         Serial.print("f:"+ valFreq+"\r\n");   
         String U = getSuply(netAdr);
         Serial.print("u:"+ U+"\r\n");   
         String A = getCurrent(netAdr);
         Serial.print("a:"+ A+"\r\n");   
         String Angle = getAngle(netAdr);
         Serial.print("g:"+ Angle+"\r\n");   
         String PowerNow = getPowerNow(netAdr);
         Serial.print("e:"+ PowerNow+"\r\n");   

       
      
     }
   

  delay(1000);
}

}


String getSerialNumber(int netAdr)
{
  String s1,s2,s3,s4;
  response[0]=0;
  Sn[0] = netAdr;
  send(Sn, sizeof(Sn),response);
  if((int)response[1] < 10) { s1="0" + String((int)response[1]); } else {s1=String((int)response[1]);}
  if((int)response[2] < 10) { s2="0" + String((int)response[2]); } else {s2=String((int)response[2]);}
  if((int)response[3] < 10) { s3="0" + String((int)response[3]); } else {s3=String((int)response[3]);}
  if((int)response[4] < 10) { s4="0" + String((int)response[4]); } else {s4=String((int)response[4]);}

  
  //String n = String((int)response[1]) + String((int)response[2]) +String((int)response[3])+ String((int)response[4]);
  String n = s1+s2+s3+s4;
  
  return String(response[0])+";"+n;
}


String getPowerNow(int netAdr)
{
 
  response[0]=0;
  Power[0] = netAdr;
  send(Power, sizeof(Power),response);
  long r = 0;
  r |= (long)response[1]<<16;
  r |= (long)response[3]<<8;
  r |= (long)response[2];
  String U0= String(r);
  r = 0;
  r |= (long)response[4]<<16;
  r |= (long)response[6]<<8;
  r |= (long)response[5];
  String U1= String(r);
  r=0;
  r |= (long)response[7]<<16;
  r |= (long)response[9]<<8;
  r |= (long)response[8];
  String U2= String(r);
  r = 0;
  r |= (long)response[10]<<16;
  r |= (long)response[12]<<8;
  r |= (long)response[11];
  String U3= String(r);
  if(response[0] == netAdr)   return String(String(response[0])+";"+U0+";"+U1+";"+U2+";"+U3);
  else   return String("Error");
 
}






String getAngle(int netAdr)
{
 
  response[0]=0;
  Angle[0] = netAdr;
  send(Angle, sizeof(Angle),response);
  long r = 0;
  r |= (long)response[1]<<16;
  r |= (long)response[3]<<8;
  r |= (long)response[2];
  String U1= String(r);
  r = 0;
  r |= (long)response[4]<<16;
  r |= (long)response[6]<<8;
  r |= (long)response[5];
  String U2= String(r);
  r=0;
  r |= (long)response[7]<<16;
  r |= (long)response[9]<<8;
  r |= (long)response[8];
  String U3= String(r);
  if(response[0] == netAdr)   return String(String(response[0])+";"+U1+";"+U2+";"+U3);
  else   return String("Error");

}


String getCurrent(int netAdr)
{
  response[0]=0;
  Current[0] = netAdr;
  send(Current, sizeof(Current),response);
  long r = 0;
  r |= (long)response[1]<<16;
  r |= (long)response[3]<<8;
  r |= (long)response[2];
  String U1= String(r);
  r = 0;
  r |= (long)response[4]<<16;
  r |= (long)response[6]<<8;
  r |= (long)response[5];
  String U2= String(r);
  r=0;
  r |= (long)response[7]<<16;
  r |= (long)response[9]<<8;
  r |= (long)response[8];
  String U3= String(r);
  if(response[0] == netAdr)   return String(String(response[0])+";"+U1+";"+U2+";"+U3);
  else   return String("Error");

}

String getSuply(int netAdr)
{
 
  response[0]=0;
  Suply[0] = netAdr;
  send(Suply, sizeof(Suply),response);
  long r = 0;
  r |= (long)response[1]<<16;
  r |= (long)response[3]<<8;
  r |= (long)response[2];
  String U1= String(r);
  r = 0;
  r |= (long)response[4]<<16;
  r |= (long)response[6]<<8;
  r |= (long)response[5];
  String U2= String(r);
  r=0;
  r |= (long)response[7]<<16;
  r |= (long)response[9]<<8;
  r |= (long)response[8];
  String U3= String(r);
  if(response[0] == netAdr)   return String(String(response[0])+";"+U1+";"+U2+";"+U3);
  else   return String("Error");

}


String getFreq(int netAdr)
{
 
  response[0]=0;
  Freq[0] = netAdr;
  send(Freq, sizeof(Freq),response);
  //String n = String((int)response[1]) + String((int)response[2]) +String((int)response[3])+ String((int)response[4]);
  long r = 0;
  r |= (long)response[1]<<16;
  r |= (long)response[3]<<8;
  r |= (long)response[2];
  String fr= String(r);
  //return fr;
  if(response[0] == netAdr)   return String(response[0])+";"+fr;
  else   return String("Error");

}

String getARPower(int netAdr)
{
  response[0]=0;
  activPower[0] = netAdr;
  send(activPower, sizeof(activPower),response);
  if(response[0] == netAdr) 
  {
  long r = 0;
  r |= (long)response[2]<<24;
  r |= (long)response[1]<<16;
  r |= (long)response[4]<<8;
  r |= (long)response[3];
  String A_plus= String(r);
  r=0;
  r |= (long)response[6]<<24;
  r |= (long)response[5]<<16;
  r |= (long)response[8]<<8;
  r |= (long)response[7];
  String A_minus= String(r);
  r = 0;
  r |= (long)response[10]<<24;
  r |= (long)response[9]<<16;
  r |= (long)response[12]<<8;
  r |= (long)response[11];
  String R_plus= String(r);
  r = 0;
  r |= (long)response[14]<<24;
  r |= (long)response[13]<<16;
  r |= (long)response[16]<<8;
  r |= (long)response[15];
  String R_minus= String(r);
  return String(String(response[0])+";"+A_plus+";"+A_minus+";"+R_plus+";"+R_minus);
  }
  //if(response[0] == netAdr)   String(A_plus+";"+A_minus+";"+R_plus+";"+R_minus);
  else   return String("Error");

  
}

//////////////////////////////////////////////////////////////////////////////////
void send(byte *cmd, int s, byte *response) {
 // Serial.print("sending...");

  unsigned int crc = crc16MODBUS(cmd, s);

  unsigned int crc1 = crc & 0xFF;
  unsigned int crc2 = (crc>>8) & 0xFF;
  delay(10);
  digitalWrite(SerialControl, RS485Transmit);  // Init Transceiver   
       for(int i=0; i<s; i++) 
       {
              RS485Serial.write(cmd[i]);
       }
  RS485Serial.write(crc1);
  RS485Serial.write(crc2);
  byte i = 0;
  digitalWrite(SerialControl, RS485Receive);  // Init Transceiver   
  delay(200);
         if (RS485Serial.available()) 
           {
             while (RS485Serial.available()) 
               {
                byteReceived= RS485Serial.read();    // Read received byte             
                delay(10);  
                response[i++] = byteReceived;
                }
           }

  
  delay(20);
}




unsigned int crc16MODBUS(byte *s, int count) {
  unsigned int crcTable[] = {
        0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
        0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
        0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
        0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
        0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
        0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
        0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
        0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
        0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
        0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
        0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
        0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
        0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
        0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
        0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
        0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
        0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
        0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
        0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
        0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
        0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
        0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
        0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
        0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
        0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
        0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
        0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
        0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
        0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
        0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
        0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
        0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040
    };

    unsigned int crc = 0xFFFF;

    for(int i = 0; i < count; i++) {
        crc = ((crc >> 8) ^ crcTable[(crc ^ s[i]) & 0xFF]);
    }

    return crc;
}