Arduino and RS485 (ENGLISH VERSION)

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NEWS => Are you interested in CAN Bus with Arduino?  Visit http://secuduino.blogspot.com/ 


RS485 is a standard serial protocol, with bus topology where you can connect several devices in a very cheap way. Here will be explained how to create a microcontrollers network just with 2 wires.


It is based in a differential couple of wires with which we can get a half-duplex comunication channel. The driver has a configurable input that provides us the possibility to set our transceiver as sender or receiver.

What do we need apart of our Arduino?
  • MAX485
  • SN75176 (cheaper)

What will be it used for? It is a voltage level converter in order to use our UART as RS485 interface.




Ok, now we are ready to start. RS485 resides in the physical layer based on the OSI Model, so it just tell us about voltages, physic parameters,....

Recommended links:

http://www.i-micro.com/pdf/articulos/rs-485.pdfdf
http://www.maxim-ic.com/appnotes.cfm?appnote_number=763&CMP=WP-1
http://www.neoteo.com/rs485-domotica-al-alcance-de-tu-mano-15810.neo-alcance-de-tu-mano-15810.neo
RS485 Oscilloscope Screenshots
http://www.sbc-support.ch/faq/files/files.get.php?ZSESSIONID=n38bphov4ls4cdsvtbd8tl6jb4&fi_index=100179

Then, we need an structural way to send our information. We will use as frames a configuration already created by Fuji in their industrial variators.

Look at: http://www.cdautomation.com/download/ENG_L_M_FUJI_RS485_COMM_for_FRENIC-Mini.PDFL_M_FUJI_RS485_COMM_for_FRENIC-Mini.PDF

Let's take a look at the frame configuration:



  • Byte 1: Start Byte ( 0 hexadecimal ).
  • Byte 2-3: ASCII Arduino's address.
  • Byte 4: Byte ENQ, ACK or NAK (0x05h, 0x06h y 0x15h) .
  • Byte 5: ASCII Requested command.
  • Byte 6 y 7: ASCII Function number.
  • Byte 8: Sign byte (Positive 0x20h y Negative 2D)
  • Byte 9-12: ASCII of data bytes (0x00h-0xFFFFh)
  • Byte 13: Byte EOT (End of Text) (0x03h)
  • Byte 14-15: Checksum (addition from 2nd byte to 13th byte)


With this configuration we have
  • 1 Byte indicating the Function Number
  • 2 Bytes indicating the sub-function Number


So imagine the possibles combinations!!! For instance:
A01 Requet of value on Analog input 1
P01 Request Configuration of PWM 1 with setup data in DATA bytes
And so on!!!! Is not wonderful?

Notice:
- Commands are ASCII Coded
- Control bytes are not ASCII Coded
It is a nice feature due to, in case we receive a 0x00 (thinking it is the start byte), the program will understand it is the starting frame instead of as 0 value, because in this case, it should be sent as ASCII (0x30).

Please take a look at the ASCII Table, even better print it! :P Probably most of us we have a copy pasted in front of us all the time, wrong?
http://www.cs.utk.edu/~pham/ascii_table.jpg




Let's see an example:
Imagine we need an arduino(master) which will decide either switch on or switch off a remote lights. Then, it have to send a command on our RS485 network and then other arduino (slave) will interpretate the command and excute it.

Then, the master will follow the switchces state, a and as needed, the master will send the frame requesting switch on/off to the slave called 01. The function will be called D and number 0.(you can set it up as needed). So,
Master sends: Slave(01)-Request execution function(D)-SubFunction(0)
0x00 0x30 0x31 0x05 0x44 0x30 0x30 0x20 0x30 0x30 0x30 0x31 0x03 0x01 0xEE
Slave answers: AKNOWLEDGE (ACK).
0x00 0x30 0x31 0x06 0x44 0x30 0x30 0x20 0x30 0x30 0x30 0x31 0x03 0x01 0xEF


The salve's ACK frame has the following configuration(take a look at Byte 4 due to here is specified ACK)

Even better, watch the following video: http://www.youtube.com/watch?v=ABcjU0Ua-d4



Urgh!!!!Sorry but the switcher is just a couple of wires going from VCC to GND! ;)

In order to see the frames flowing on the net, you need just a USB <----> RS232 like FTDI232 or MAX232+MAX485,... If you have an Arduino PCB, notice you can remove the uC from its socket and you'll have an USB <---->Rs232 converter!


If you want to monitorize what is going on , you can use Hyperterminal, or any one that include some useful features as format output, saving options,....for instance we like:
RealTerm
FREE SERIAL TERMINAL MONITOR
Really nice if you want to sniff RS232 frames

In this example we have 3 arduinos connected. The master have 2 switchers used to switch on/off leds connected to each of the slaves.
.




Let's see how it works: http://www.youtube.com/watch?v=S9FSQaToVZ4


Now...THE CODE!

IMPORTANT:
Checksum are done directly in hex instead of convert it to ASCII. Change it could be necessary , to don't have problems. This entry is a howto paper to show you how RS485 works and explain how to implemnt a protocol, but is not 100% debbuged.



MASTER:


//----------------------------------
//RS 485
//By Igor Real
//24-06-09
//----------------------------------


byte            data[12];
unsigned long   previous_time;
unsigned long   previous_time2;
byte            times_repeat=5;
byte            times_repeat2=5;

byte            state=0;
byte            state2=0;

#define  pinCONTROL    02
#define  myaddress     01
  

void setup() {

   pinMode(13,OUTPUT);
   pinMode(pinCONTROL,OUTPUT);
   digitalWrite(13,HIGH);
   digitalWrite(12,LOW);
   pinMode(8,INPUT);
   pinMode(9,INPUT);
   digitalWrite(pinCONTROL,LOW);
   Serial.begin(9600);
   Serial.println("Empezamos");
   state=0;
   state2=0;
}

void loop()
{

  if (digitalRead(8)==state){
    state=!state;
    times_repeat=0;  
  }
  if (digitalRead(9)==state2){
    state2=!state2;
    times_repeat2=0;  
  }

  
  
  
  if (times_repeat<4){
    Serial.flush();  
    //(byte address1,byte address2,byte data_type,byte code1,byte code2,byte Sign,byte data1,byte data2,byte data3,byte data4)
    if (digitalRead(8)==HIGH){  
      sendMSG(48,49,68,48,48,32,48,48,48,49);
    }else {
      sendMSG(48,49,68,48,48,32,48,48,48,48);
    }
    times_repeat=times_repeat+1;
  
    previous_time=millis();
    while (((millis()-previous_time)<500) && (Serial.available()!=15)){
      ;;
    }
  
    if (Serial.available()>=15){
      if (receiveMSG()==1){
        Serial.println("Trama correcta");
        if (data[0]==48 && data[1]==49 && data[2]==6){
          //ACK  
          times_repeat=5;
          Serial.println("ACK recibido");
        }
      }
     }
   }  
  
  

  if (times_repeat2<4){
    Serial.flush();  
    //(byte address1,byte address2,byte data_type,byte code1,byte code2,byte Sign,byte data1,byte data2,byte data3,byte data4)
    if (digitalRead(9)==HIGH){  
      sendMSG(48,50,68,48,48,32,48,48,48,49);
    }else {
      sendMSG(48,50,68,48,48,32,48,48,48,48);
    }
    times_repeat2=times_repeat2+1;
  
    previous_time2=millis();
    while (((millis()-previous_time2)<500) && (Serial.available()!=15)){
    ;;
    }
  
    if (Serial.available()>=15){
      if (receiveMSG()==1){
        //Serial.println("Trama correcta");
        if (data[0]==48 && data[1]==50 && data[2]==6){
          //ACK  
          times_repeat2=5;
          //Serial.println("ACK recibido");
        }
      }
    }
  }
  
  
  
}


//------------------------
//FUNCIONES
//------------------------

byte receiveMSG(){

  byte  byte_receive;
  byte  state=0;
  byte  cont1=1;
  byte  trace_OK=0;

  unsigned int checksum;
  unsigned int checksum_trace;
  
  
  
  while (Serial.available() > 0){
    
     byte_receive=Serial.read();
     if (byte_receive==00){
       state=1;
       checksum_trace=0;
       checksum=0;
       trace_OK=0;
       cont1=1;
     }else if (state==1 && cont1<=12){
       data[cont1-1]=byte_receive;
       checksum=checksum+byte_receive;
       cont1=cont1+1;
     }else if (state==1 && cont1==13){
       checksum_trace=byte_receive<<8;
       cont1=cont1+1;
     }else if (state==1 && cont1==14){
       checksum_trace=checksum_trace+byte_receive;
       cont1=cont1+1;
       state=0;
       if (checksum_trace==checksum){
           trace_OK=1;
       }else{
         trace_OK=0;
       }
       break;
     }
  }
  return trace_OK;

}



void sendMSG(byte address1,byte address2,byte data_type,byte code1,byte code2,byte Sign,byte data1,byte data2,byte data3,byte data4){
  
  unsigned int checksum_ACK;
  checksum_ACK=address1+address2+5+data_type+code1+code2+Sign+data1+data2+data3+data4+3;
  
  UCSR0A=UCSR0A |(1 << TXC0);
  
  digitalWrite(pinCONTROL,HIGH);
  delay(1);

  Serial.print(0,BYTE);
  Serial.print(address1,BYTE);
  Serial.print(address2,BYTE);
  Serial.print(5,BYTE);
  Serial.print(data_type,BYTE);
  Serial.print(code1,BYTE);
  Serial.print(code2,BYTE);
  Serial.print(Sign,BYTE);
  Serial.print(data1,BYTE);
  Serial.print(data2,BYTE);
  Serial.print(data3,BYTE);
  Serial.print(data4,BYTE);  
  Serial.print(3,BYTE);
  Serial.print(((checksum_ACK>>8)&255),BYTE);
  Serial.print(((checksum_ACK)& 255),BYTE);
  while (!(UCSR0A & (1 << TXC0)));
  digitalWrite(pinCONTROL,LOW);

  
  
}



void sendACK(byte address1,byte address2,byte data_type,byte code1,byte code2,byte Sign,byte data1,byte data2,byte data3,byte data4){
  
  unsigned int checksum_ACK;
  checksum_ACK=address1+address2+6+data_type+code1+code2+Sign+data1+data2+data3+data4+3;
  
  UCSR0A=UCSR0A |(1 << TXC0);
  
  digitalWrite(pinCONTROL,HIGH);
  delay(1);

  Serial.print(0,BYTE);
  Serial.print(address1,BYTE);
  Serial.print(address2,BYTE);
  Serial.print(6,BYTE);
  Serial.print(data_type,BYTE);
  Serial.print(code1,BYTE);
  Serial.print(code2,BYTE);
  Serial.print(Sign,BYTE);
  Serial.print(data1,BYTE);
  Serial.print(data2,BYTE);
  Serial.print(data3,BYTE);
  Serial.print(data4,BYTE);  
  Serial.print(3,BYTE);
  Serial.print(((checksum_ACK>>8)&255),BYTE);
  Serial.print(((checksum_ACK)&255),BYTE);
  while (!(UCSR0A & (1 << TXC0)));
  digitalWrite(pinCONTROL,LOW);
  
  
}

void sendNAK(byte address1,byte address2,byte data_type,byte code1,byte code2,byte Sign,byte data1,byte data2,byte data3,byte data4){
  
  unsigned int checksum_ACK;
  checksum_ACK=address1+address2+6+data_type+code1+code2+Sign+data1+data2+data3+data4+3;
  
  UCSR0A=UCSR0A |(1 << TXC0);
  
  digitalWrite(pinCONTROL,HIGH);
  delay(1);

  Serial.print(0,BYTE);
  Serial.print(address1,BYTE);
  Serial.print(address2,BYTE);
  Serial.print(15,BYTE);
  Serial.print(data_type,BYTE);
  Serial.print(code1,BYTE);
  Serial.print(code2,BYTE);
  Serial.print(Sign,BYTE);
  Serial.print(data1,BYTE);
  Serial.print(data2,BYTE);
  Serial.print(data3,BYTE);
  Serial.print(data4,BYTE);  
  Serial.print(3,BYTE);
  Serial.print(((checksum_ACK>>8)&255),BYTE);
  Serial.print(((checksum_ACK)&255),BYTE);
  while (!(UCSR0A & (1 << TXC0)));
  digitalWrite(pinCONTROL,LOW);
  
  
}



byte hex2num(byte x){

  byte result;
  
  if (x>=48 && x<=57){
    result=x-48;  
  }else if (x>=65 && x<=70){
    switch(x){
      case 65:
        result=10;
        break;
      case 66:
        result=11;
        break;
      case 67:
        result=12;
        break;
      case 68:
        result=13;
        break;
      case 69:
        result=14;
        break;
      case 70:
        result=15;
        break;    
    }  
  }
  return result;  
}



 

SLAVES:
(you have to change myaddress to 01 or 02)


//----------------------------------
//RS 485
//By Igor Real
//24-06-09
//----------------------------------


byte  data[12];
byte  address;
byte  function;
byte  function_code;
unsigned int data_received;
byte  byte_receive;
byte  state=0;
byte  cont1=1;
byte  trace_OK=0;
unsigned int checksum;
unsigned int checksum_trace;

#define  pinCONTROL    02
#define  myaddress     02
  

void setup() {

   pinMode(13,OUTPUT);
   pinMode(pinCONTROL,OUTPUT);
   digitalWrite(2,LOW);
   Serial.begin(9600);
   Serial.println("Empezamos");

}

void loop()
{

   while (Serial.available() > 0){
    
     byte_receive=Serial.read();
     if (byte_receive==00){
       //Serial.println("Se ha recibido byte Start");
       state=1;
       checksum_trace=0;
       checksum=0;
       trace_OK=0;
       address=0;
       data_received=0;
       cont1=1;
     }else if (state==1 && cont1<=12){
       data[cont1-1]=byte_receive;
       checksum=checksum+byte_receive;
       cont1=cont1+1;
     }else if (state==1 && cont1==13){
       checksum_trace=byte_receive<<8;
       cont1=cont1+1;
       //Serial.print("Primer Byte Checksum");      
       //Serial.print(checksum_trace,HEX);
     }else if (state==1 && cont1==14){
       checksum_trace=checksum_trace+byte_receive;
       cont1=cont1+1;
       state=0;
       //Serial.println(byte_receive,HEX);
       //Serial.println("Recibida trama");
       //Serial.print("Checksum Trace= ");
       //Serial.println(checksum_trace,HEX);
       //Serial.print("Checksum= ");
       //Serial.println(checksum,HEX);
       //Serial.println(checksum,DEC);
       //Serial.println("Trama= ");
       //Serial.print(data[0]);
       //Serial.print(data[1]);
       //Serial.print(data[2]);
       //Serial.print(data[3]);
       //Serial.print(data[4]);
       //Serial.print(data[5]);
       //Serial.print(data[6]);
       //Serial.print(data[7]);
       //Serial.print(data[8]);
       //Serial.print(data[9]);
       //Serial.print(data[10]);
       //Serial.println(data[11]);      

       if (checksum_trace==checksum){
         trace_OK=1;
        
         address=(hex2num(data[0])<<4)+(hex2num(data[1]));
         function=data[3];
         function_code=(hex2num(data[4])<<4)+(hex2num(data[5]));
         data_received=(hex2num(data[7])<<12)+(hex2num(data[8])<<8)+(hex2num(data[9])<<4)+(hex2num(data[10]));
        
         //Serial.println("TRAZA CORRECTA");
         //Serial.println(address,DEC);
         //Serial.println(data_received);
         if (address==myaddress){
           if ((function=='D') && (function_code==0) && data[2]==5){
             if (data_received==1){
               digitalWrite(13,HIGH);
               //Serial.println(data_received,DEC);
               sendACK(data[0],data[1],data[3],data[4],data[5],data[6],data[7],data[8],data[9],data[10]);
             }else if (data_received==0){
               digitalWrite(13,LOW);
               sendACK(data[0],data[1],data[3],data[4],data[5],data[6],data[7],data[8],data[9],data[10]);
             }
           }
         }
       }else{
         //Serial.println("TRAZA INCORRECTA");  
         sendNAK(data[0],data[1],data[3],data[4],data[5],data[6],data[7],data[8],data[9],data[10]);
       }
     }

  }
  
}


//------------------------
//FUNCIONES
//------------------------

byte receiveMSG(){

  byte  byte_receive;
  byte  state=0;
  byte  cont1=1;
  byte  trace_OK=0;

  unsigned int checksum;
  unsigned int checksum_trace;
  

  
  
  while (Serial.available() > 0){
    
     byte_receive=Serial.read();
     if (byte_receive==00){
       state=1;
       checksum_trace=0;
       checksum=0;
       trace_OK=0;
       cont1=1;
     }else if (state==1 && cont1<=12){
       data[cont1-1]=byte_receive;
       checksum=checksum+byte_receive;
       cont1=cont1+1;
     }else if (state==1 && cont1==13){
       checksum_trace=byte_receive<<8;
       cont1=cont1+1;
     }else if (state==1 && cont1==14){
       checksum_trace=checksum_trace+byte_receive;
       cont1=cont1+1;
       state=0;
       if (checksum_trace==checksum){
           trace_OK=1;
       }else{
         trace_OK=0;
       }
       break;
     }
  }
  return trace_OK;

}



void sendMSG(byte address1,byte address2,byte data_type,byte code1,byte code2,byte Sign,byte data1,byte data2,byte data3,byte data4){
  
  unsigned int checksum_ACK;
  checksum_ACK=address1+address2+5+data_type+code1+code2+Sign+data1+data2+data3+data4+3;
  
  UCSR0A=UCSR0A |(1 << TXC0);
  
  digitalWrite(pinCONTROL,HIGH);
  delay(1);

  Serial.print(0,BYTE);
  Serial.print(address1,BYTE);
  Serial.print(address2,BYTE);
  Serial.print(5,BYTE);
  Serial.print(data_type,BYTE);
  Serial.print(code1,BYTE);
  Serial.print(code2,BYTE);
  Serial.print(Sign,BYTE);
  Serial.print(data1,BYTE);
  Serial.print(data2,BYTE);
  Serial.print(data3,BYTE);
  Serial.print(data4,BYTE);  
  Serial.print(3,BYTE);
  Serial.print(((checksum_ACK>>8)&255),BYTE);
  Serial.print(((checksum_ACK)& 255),BYTE);
  while (!(UCSR0A & (1 << TXC0)));
  digitalWrite(pinCONTROL,LOW);

  
  
}



void sendACK(byte address1,byte address2,byte data_type,byte code1,byte code2,byte Sign,byte data1,byte data2,byte data3,byte data4){
  
  unsigned int checksum_ACK;
  checksum_ACK=address1+address2+6+data_type+code1+code2+Sign+data1+data2+data3+data4+3;
  
  UCSR0A=UCSR0A |(1 << TXC0);
  
  digitalWrite(pinCONTROL,HIGH);
  delay(1);

  Serial.print(0,BYTE);
  Serial.print(address1,BYTE);
  Serial.print(address2,BYTE);
  Serial.print(6,BYTE);
  Serial.print(data_type,BYTE);
  Serial.print(code1,BYTE);
  Serial.print(code2,BYTE);
  Serial.print(Sign,BYTE);
  Serial.print(data1,BYTE);
  Serial.print(data2,BYTE);
  Serial.print(data3,BYTE);
  Serial.print(data4,BYTE);  
  Serial.print(3,BYTE);
  Serial.print(((checksum_ACK>>8)&255),BYTE);
  Serial.print(((checksum_ACK)&255),BYTE);
  while (!(UCSR0A & (1 << TXC0)));
  digitalWrite(pinCONTROL,LOW);
  
  
}

void sendNAK(byte address1,byte address2,byte data_type,byte code1,byte code2,byte Sign,byte data1,byte data2,byte data3,byte data4){
  
  unsigned int checksum_ACK;
  checksum_ACK=address1+address2+6+data_type+code1+code2+Sign+data1+data2+data3+data4+3;
  
  UCSR0A=UCSR0A |(1 << TXC0);
  
  digitalWrite(pinCONTROL,HIGH);
  delay(1);

  Serial.print(0,BYTE);
  Serial.print(address1,BYTE);
  Serial.print(address2,BYTE);
  Serial.print(15,BYTE);
  Serial.print(data_type,BYTE);
  Serial.print(code1,BYTE);
  Serial.print(code2,BYTE);
  Serial.print(Sign,BYTE);
  Serial.print(data1,BYTE);
  Serial.print(data2,BYTE);
  Serial.print(data3,BYTE);
  Serial.print(data4,BYTE);  
  Serial.print(3,BYTE);
  Serial.print(((checksum_ACK>>8)&255),BYTE);
  Serial.print(((checksum_ACK)&255),BYTE);
  while (!(UCSR0A & (1 << TXC0)));
  digitalWrite(pinCONTROL,LOW);
  
  
}



byte hex2num(byte x){

  byte result;
  
  if (x>=48 && x<=57){
    result=x-48;  
  }else if (x>=65 && x<=70){
    switch(x){
      case 65:
        result=10;
        break;
      case 66:
        result=11;
        break;
      case 67:
        result=12;
        break;
      case 68:
        result=13;
        break;
      case 69:
        result=14;
        break;
      case 70:
        result=15;
        break;    
    }  
  }
  return result;  
}



Now, we will learn how to wire a bus topology:
.
 
.
Each Arduino or gadget conneted to the net, is wired with an Y welded which comes out 2 connectors from same family different kind(Male/female). The shorter the better. Each connector will have VCC,Sginal A, Singal B and GND. This way, if we want to connect another device onto the net, you need just insert each device or put it at the end. Now is easy understand why we are putting a Y , it's extremely easy connect and disconnect a device from the bus, due to each device has male an female. Is worthy have always a couple of connectors with a end-resistor between Singal A and Signal B RS485 pins in order to "close" the wires' end. If we need add another device is as easy as disconnet the connector with the end-resistor, insert the new device and close again with that connector. Wire VCC and GND is extremely easy, and in future, will make things really easier in possible expansions..... Take care, and twist Signal A and Signal B wires. Please take a loot at next link if needed : http://www.rs-485.com/download/485%20network%20topology.pdf
.
This paper was based on spanish Igor R's one. Thanks Igor R!! Cheers!!!
.
.
Aritz R.
.
.

18 comentarios:

  1. This is just as a note for other people:

    It took me a while to realize that you need to connect the write enable and read enable lines to the digital pin 2 on the microcontroller.

    ResponderEliminar
  2. Hi,

    Please, find below the pin out of the MAX485 (DIP-8)

    PIN-OUT MAX485 --> Arduino
    1 -> RO (Receiver Output) to pin 0 (Rx)
    2 -> Receive enable to a digital input (ej: pin2)
    3 -> Driver enable to a digital (ej:pin2)
    4 -> DI (Driver In) to pin 1 (Tx)
    5 -> GND to gnd of the arduino
    6 -> SIGNAL A (bus RS-485)
    7 -> SIGNAL B (bus RS-485)
    8 -> Vcc to 5 voltios of the arduino



    Regards,



    Igor

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  3. This is great, I've been looking for this for a while! Good detailed explination.

    Thanks from NL
    Rob

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  4. Nice tutorial!

    question:
    is it possible to sent data from the slave to the master in the ACK (in the byte 9 .. 12)?

    Floris at deboktor dot nl

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  5. Hi Floris,
    Of course you can. It´s the designer who decides how the protocol works. It´s 100% open.
    The RS485 only defines the phisical layer.

    Cheers!!


    Igor

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  6. Hi Igor,
    Thanks for your work.

    I semplified your code, it is easier to mantain it too:

    void sendACK_NAK(byte type,byte address1,byte address2,byte data_type,byte code1,byte code2,byte Sign,byte data1,byte data2,byte data3,byte data4){

    unsigned int checksum_ACK;
    checksum_ACK=address1+address2+6+data_type+code1+code2+Sign+data1+data2+data3+data4+3;

    UCSR0A=UCSR0A |(1 << TXC0);

    digitalWrite(pinCONTROL,HIGH);
    delay(1);

    Serial.print(0,BYTE);
    Serial.print(address1,BYTE);
    Serial.print(address2,BYTE);
    Serial.print(type,BYTE);
    Serial.print(data_type,BYTE);
    Serial.print(code1,BYTE);
    Serial.print(code2,BYTE);
    Serial.print(Sign,BYTE);
    Serial.print(data1,BYTE);
    Serial.print(data2,BYTE);
    Serial.print(data3,BYTE);
    Serial.print(data4,BYTE);
    Serial.print(3,BYTE);
    Serial.print(((checksum_ACK>>8)&255),BYTE);
    Serial.print(((checksum_ACK)&255),BYTE);
    while (!(UCSR0A & (1 << TXC0)));
    digitalWrite(pinCONTROL,LOW);
    }

    void sendACK(byte address1,byte address2,byte data_type,byte code1,byte code2,byte Sign,byte data1,byte data2,byte data3,byte data4){
    sendACK_NAK(6, address1, address2, data_type, code1, code2, Sign, data1, data2, data3, data4);
    }


    void sendNAK(byte address1,byte address2,byte data_type,byte code1,byte code2,byte Sign,byte data1,byte data2,byte data3,byte data4){
    sendACK_NAK(15, address1, address2, data_type, code1, code2, Sign, data1, data2, data3, data4);
    }

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    Respuestas
    1. Giangi,
      Corrected sendNAK should have been as below (because NAK = 0x15 = 21:

      void sendNAK(byte address1,byte address2,byte data_type,byte code1,byte code2,byte Sign,byte data1,byte data2,byte data3,byte data4){
      sendACK_NAK(21, address1, address2, data_type, code1, code2, Sign, data1, data2, data3, data4);
      }

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  7. And this one too:


    byte hex2num(byte x){
    byte result;

    if (x>=48 && x<=57){ //numbers 0-9
    result=x-48;
    }else if (x>=65 && x<=70){ //A-F
    result=x-55; //A=10, B=11, …,F=15
    }
    return result;
    }

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  8. Igor I think there is a bug in the original sendNAK function.
    Should the row
    checksum_ACK=address1+address2+6+data_type+code1+code2+Sign+data1+data2+data3+data4+3;
    be corrected in
    checksum_ACK=address1+address2+21+data_type+code1+code2+Sign+data1+data2+data3+data4+3;
    ?
    Notice the 21 value (0x15h) instead of 6 because you wrote ENQ, ACK or NAK (0x05h, 0x06h y 0x15h).

    In this case the code is much simplier because you can merge the sendMSG code too:

    void sendMSG(byte type, byte address1,byte address2,byte data_type,byte code1,byte code2,byte Sign,byte data1,byte data2,byte data3,byte data4){

    unsigned int checksum_ACK;
    checksum_ACK=address1+address2+type+data_type+code1+code2+Sign+data1+data2+data3+data4+3;

    UCSR0A=UCSR0A |(1 << TXC0);

    digitalWrite(pinCONTROL,HIGH);
    delay(1);

    Serial.print(0,BYTE);
    Serial.print(address1,BYTE);
    Serial.print(address2,BYTE);
    Serial.print(type,BYTE);
    Serial.print(data_type,BYTE);
    Serial.print(code1,BYTE);
    Serial.print(code2,BYTE);
    Serial.print(Sign,BYTE);
    Serial.print(data1,BYTE);
    Serial.print(data2,BYTE);
    Serial.print(data3,BYTE);
    Serial.print(data4,BYTE);
    Serial.print(3,BYTE);
    Serial.print(((checksum_ACK>>8)&255),BYTE);
    Serial.print(((checksum_ACK)&255),BYTE);
    while (!(UCSR0A & (1 << TXC0)));
    digitalWrite(pinCONTROL,LOW);
    }

    void sendACK(byte address1,byte address2,byte data_type,byte code1,byte code2,byte Sign,byte data1,byte data2,byte data3,byte data4){
    sendMSG(6, address1, address2, data_type, code1, code2, Sign, data1, data2, data3, data4);
    }


    void sendNAK(byte address1,byte address2,byte data_type,byte code1,byte code2,byte Sign,byte data1,byte data2,byte data3,byte data4){
    sendMSG(15, address1, address2, data_type, code1, code2, Sign, data1, data2, data3, data4);
    }

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  9. Good points Giangi!! Please feel free to send me your improvements and I can publish them here.

    Thanks!

    ;)

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  10. Hi,

    I'm wondering if there won't be any problems with addresses if I set master to 01 and slaves as u wrote 01 and 02. Shouldn't be for ex. master 01, slave_1 02, and slave_2 03 ??

    I hope it isn't a stupid question - I'm just starting with it

    cheers.

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  11. Hi,
    can send me a schematic to build this? Where to put the resistor and where the jumper?

    Thank You

    Andreas

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  12. Hi,
    Could you please post a schematic of how you wired the led and the pushbutton?

    Thank's,
    Cristian

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  13. Hello, thanks for your post.
    I've tried to implement the same circuit, but I'm facing a problem to use the Arduino as USB->Serial converter. I just receive datas in the PC, but I'm not able to send datas from it.
    Could you help me?
    Thanks

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  14. Hello, I'd like to know, which are the parts of the whole message that I can use to communicate the commands?

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  15. Hello Well done for this nice job ! ! !

    I would like to ask if it is possibly to make a library so less code need to use in the IDE.

    Thank you.

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  16. Noob question:

    I want to connect several sensors to an Arduino, but each sensor will be far from it, like 20 to 30 meters. Is it possible to send the sensor data (ultrasound/temp) via RS485?

    Thanks,

    Alvaro

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