MODBUS protocol.

Thread Starter

ajitnayak

Joined Feb 22, 2013
42
Dear all,

I am trying to interface modbus protcol with Arduino . I downloaded the library form Below links.How to give slave ID, address ,function code and CHeck output for program below. along with wiring diagram.



https://code.google.com/p/simple-modbus/.

http://code.google.com/p/arduino-modbus-slave/downloads/detail?name=MODBUS.zip&can=2&q=.



Rich (BB code):
#include <SimpleModbusSlave.h>

/* This example code will receive the adc ch0 value from the arduino master. 
   It will then use this value to adjust the brightness of the led on pin 9.
   The value received from the master will be stored in address 1 in its own
   address space namely holdingRegs[].
   
   In addition to this the slaves own adc ch0 value will be stored in 
   address 0 in its own address space holdingRegs[] for the master to
   be read. The master will use this value to alter the brightness of its
   own led connected to pin 9.
   
   The modbus_update() method updates the holdingRegs register array and checks
   communication.

   Note:  
   The Arduino serial ring buffer is 128 bytes or 64 registers.
   Most of the time you will connect the arduino to a master via serial
   using a MAX485 or similar.
 
   In a function 3 request the master will attempt to read from your
   slave and since 5 bytes is already used for ID, FUNCTION, NO OF BYTES
   and two BYTES CRC the master can only request 122 bytes or 61 registers.
 
   In a function 16 request the master will attempt to write to your 
   slave and since a 9 bytes is already used for ID, FUNCTION, ADDRESS, 
   NO OF REGISTERS, NO OF BYTES and two BYTES CRC the master can only write
   118 bytes or 59 registers.
 
   Using a USB to Serial converter the maximum bytes you can send is 
   limited to its internal buffer which differs between manufactures. 
*/

#define  LED 13  

// Using the enum instruction allows for an easy method for adding and 
// removing registers. Doing it this way saves you #defining the size 
// of your slaves register array each time you want to add more registers
// and at a glimpse informs you of your slaves register layout.

//////////////// registers of your slave ///////////////////
enum 
{     
  // just add or remove registers and your good to go...
  // The first register starts at address 0
  ADC_VAL,     
  PWM_VAL,        
  HOLDING_REGS_SIZE // leave this one
  // total number of registers for function 3 and 16 share the same register array
  // i.e. the same address space
};

unsigned int holdingRegs[HOLDING_REGS_SIZE]; // function 3 and 16 register array
////////////////////////////////////////////////////////////

void setup()
{
  /* parameters(HardwareSerial* SerialPort,
                long baudrate, 
		unsigned char byteFormat,
                unsigned char ID, 
                unsigned char transmit enable pin, 
                unsigned int holding registers size,
                unsigned int* holding register array)
  */
  
  /* Valid modbus byte formats are:
     SERIAL_8N2: 1 start bit, 8 data bits, 2 stop bits
     SERIAL_8E1: 1 start bit, 8 data bits, 1 Even parity bit, 1 stop bit
     SERIAL_8O1: 1 start bit, 8 data bits, 1 Odd parity bit, 1 stop bit
     
     You can obviously use SERIAL_8N1 but this does not adhere to the
     Modbus specifications. That said, I have tested the SERIAL_8N1 option 
     on various commercial masters and slaves that were suppose to adhere
     to this specification and was always able to communicate... Go figure.
     
     These byte formats are already defined in the Arduino global name space. 
  */
	

  modbus_configure(9600, 1, 2, HOLDING_REGS_SIZE, holdingRegs); 
  pinMode(LED, OUTPUT);
}

void loop()
{
  // modbus_update() is the only method used in loop(). It returns the total error
  // count since the slave started. You don't have to use it but it's useful
  // for fault finding by the modbus master.
  
  modbus_update();
  
  holdingRegs[ADC_VAL] = analogRead(A0); // update data to be read by the master to adjust the PWM
  
  analogWrite(LED, holdingRegs[PWM_VAL]>>2); // constrain adc value from the arduino master to 255
  
  /* Note:
     The use of the enum instruction is not needed. You could set a maximum allowable
     size for holdinRegs[] by defining HOLDING_REGS_SIZE using a constant and then access 
     holdingRegs[] by "Index" addressing. 
     I.e.
     holdingRegs[0] = analogRead(A0);
     analogWrite(LED, holdingRegs[1]/4);
  */
  
}
code 2
Rich (BB code):
#include <modbus.h>
#include <modbusDevice.h>
#include <modbusRegBank.h>
#include <modbusSlave.h>

/*
This example code shows a quick and dirty way to get an
arduino to talk to a modbus master device with a
device ID of 1 at 9600 baud.
*/

//Setup the brewtrollers register bank
//All of the data accumulated will be stored here
modbusDevice regBank;
//Create the modbus slave protocol handler
modbusSlave slave;

void setup()
{   

//Assign the modbus device ID.  
  regBank.setId(1);

/*
modbus registers follow the following format
00001-09999  Digital Outputs, A master device can read and write to these registers
10001-19999  Digital Inputs, A master device can only read the values from these registers
30001-39999  Analog Inputs, A master device can only read the values from these registers
40001-49999  Analog Outputs, A master device can read and write to these registers 

Analog values are 16 bit unsigned words stored with a range of 0-32767
Digital values are stored as bytes, a zero value is OFF and any nonzer value is ON

It is best to configure registers of like type into contiguous blocks.  this
allows for more efficient register lookup and and reduces the number of messages
required by the master to retrieve the data
*/

//Add Digital Output registers 00001-00016 to the register bank
  regBank.add(1);
  regBank.add(2);
  regBank.add(3);
  regBank.add(4);
  regBank.add(5);
  regBank.add(6);
  regBank.add(7);
  regBank.add(8);
  regBank.add(9);
  regBank.add(10);
  regBank.add(11);
  regBank.add(12);
  regBank.add(13);
  regBank.add(14);
  regBank.add(15);
  regBank.add(16);

//Add Digital Input registers 10001-10008 to the register bank
  regBank.add(10001);  
  regBank.add(10002);  
  regBank.add(10003);  
  regBank.add(10004);  
  regBank.add(10005);  
  regBank.add(10006);  
  regBank.add(10007);  
  regBank.add(10008);  

//Add Analog Input registers 30001-10010 to the register bank
  regBank.add(30001);  
  regBank.add(30002);  
  regBank.add(30003);  
  regBank.add(30004);  
  regBank.add(30005);  
  regBank.add(30006);  
  regBank.add(30007);  
  regBank.add(30008);  
  regBank.add(30009);  
  regBank.add(30010);  

//Add Analog Output registers 40001-40020 to the register bank
  regBank.add(40001);  
  regBank.add(40002);  
  regBank.add(40003);  
  regBank.add(40004);  
  regBank.add(40005);  
  regBank.add(40006);  
  regBank.add(40007);  
  regBank.add(40008);  
  regBank.add(40009);  
  regBank.add(40010);  
  regBank.add(40011);  
  regBank.add(40012);  
  regBank.add(40013);  
  regBank.add(40014);  
  regBank.add(40015);  
  regBank.add(40016);  
  regBank.add(40017);  
  regBank.add(40018);  
  regBank.add(40019);  
  regBank.add(40020);  

/*
Assign the modbus device object to the protocol handler
This is where the protocol handler will look to read and write
register data.  Currently, a modbus slave protocol handler may
only have one device assigned to it.
*/
  slave._device = &regBank;  

// Initialize the serial port for coms at 9600 baud  
  slave.setBaud(9600);   
}

void loop()
{
//put some data into the registers
  regBank.set(1, 1);  
  regBank.set(2, 1);  
  regBank.set(3, 0);  
  regBank.set(4, 1);  
  regBank.set(5, 1);  
  regBank.set(6, 0);  
  regBank.set(7, 1);  
  regBank.set(8, 0);  

  regBank.set(10001, 1);
  regBank.set(10002, 1);  
  regBank.set(10003, 1);  
  regBank.set(10004, 1);  
  regBank.set(10005, 0);  
  regBank.set(10006, 0);  
  regBank.set(10007, 0);  
  regBank.set(10008, 0);  


  regBank.set(30001,1);
  regBank.set(30002,2);
  regBank.set(30003,3);
  regBank.set(30004,4);
  regBank.set(30005,5);
  regBank.set(30006,6);
  regBank.set(30007,7);
  regBank.set(30008,8);
  regBank.set(30009,9);
  regBank.set(30010,10);

  regBank.set(40001,1);
  regBank.set(40002,2);
  regBank.set(40003,2);
  regBank.set(40004,4);
  regBank.set(40005,5);
  regBank.set(40006,6);
  regBank.set(40007,7);
  regBank.set(40008,8);
  regBank.set(40009,9);
  regBank.set(40010,10);
  
 while(1)
  {
    //put a random number into registers 1, 10001, 30001 and 40001
    regBank.set(1, (byte) random(0, 2));
    regBank.set(10001, (byte) random(0, 2));
    regBank.set(30001, (word) random(0, 32767));
    regBank.set(40001, (word) random(0, 32767));
    
     slave.run();  
  }
}
 

Attachments

HDowns

Joined Nov 24, 2010
5
You are truing the "Slave" library. This slave code responds to all requests (with all addresses) and supports only the function code #3 (holding registers).
 

Thread Starter

ajitnayak

Joined Feb 22, 2013
42
How to assign the value to slave address and that can be retentive from master later.
I have
Rich (BB code):
analog 2 : wind sensor and temperature sensor
RTC signal: A4 and A5 which give date and time
Some Serial value like zenith,azimuth ,Desired angle . Which are floating
value. How can i assign to slave address.
Can i change slave address like 40001 instead 4001???
 
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