I have seen a few posts lately on MODBUS so I thought I might post what I use with arduino.
The library I use is located here:
http://code.google.com/p/arduino-modbus-slave/downloads/detail?name=MODBUS.zip&can=2&q=
I have multiple slaves running. I use the code posted below on ALL of them, all I change is the slave ID. I keep all the pins the same, that way when I upload this code onto ANY arduino, it works. You should not have to change ANYTHING ELSE!
I also have this running over Xbee's through a Digi Connectport X4, which converts it to TCP. I then use Mango M2M as my SCADA package. I can now get my Analog and digital data from anywhere in the world, or open and close my roller doors, anything. I can even write Analog values. All my logic is done in Mango. You could probably do a mesh with a Xbee as a coordinator on a PC, transmitting to all the MODBUS slaves,(leave all destination addresses as zero's and set the slave Xbees to routers), but have not tried it because I have an X4
I DO NOT think you need to use RS485 for this. Just connect a PC straight up to your freshly programmed arduino, and run some sort of MODBUS master or test software, using the register number as listed in the code. Remember, in the SCADA software do not use the whole address number, for instance, to access pin 2, you would be reading a COIL on Slave 1 at address 2, not address 10002. Some SCADA packages use ZERO offsets, so subtract 1, so the address for pin 2 would be 1.
#include <modbus.h>
#include <modbusDevice.h>
#include <modbusRegBank.h>
#include <modbusSlave.h>
/* PINS
Add more registers if needed
Digital input pins 2,3,4,5,6,7
Digital output pins 8,9,12,13
Analog output pins 10,11 (PWM)
Analog input pins 0,1,2,3,4,5
*/
modbusDevice regBank;
modbusSlave slave;
int AI0,AI1,AI2,AI3,AI4,AI5;
void setup()
{
regBank.setId(1); ///Set Slave ID
//Add Digital Input registers
regBank.add(10002);
regBank.add(10003);
regBank.add(10004);
regBank.add(10005);
regBank.add(10006);
regBank.add(10007);
// Add Digital Output registers
regBank.add(8);
regBank.add(9);
regBank.add(12);
regBank.add(13);
//Analog input registers
regBank.add(30001);
regBank.add(30002);
regBank.add(30003);
regBank.add(30004);
regBank.add(30005);
regBank.add(30006);
//Analog Output registers
regBank.add(40010);
regBank.add(40011);
slave._device = ®Bank;
slave.setBaud(9600);
pinMode(2,INPUT);
pinMode(3,INPUT);
pinMode(4,INPUT);
pinMode(5,INPUT);
pinMode(6,INPUT);
pinMode(7,INPUT);
pinMode(8,OUTPUT);
pinMode(9,OUTPUT);
pinMode(12,OUTPUT);
pinMode(13,OUTPUT);
}
void loop(){
while(1){
//Digital Input
byte DI2 = digitalRead(2);
if (DI2 >= 1)regBank.set(10002,1);
if (DI2 <= 0)regBank.set(10002,0);
byte DI3 = digitalRead(3);
if (DI3 >= 1)regBank.set(10003,1);
if (DI3 <= 0)regBank.set(10003,0);
byte DI4 = digitalRead(4);
if (DI4 >= 1)regBank.set(10004,1);
if (DI4 <= 0)regBank.set(10004,0);
byte DI5 = digitalRead(5);
if (DI5 >= 1)regBank.set(10005,1);
if (DI5 <= 0)regBank.set(10005,0);
byte DI6 = digitalRead(6);
if (DI6 >= 1)regBank.set(10006,1);
if (DI6 <= 0)regBank.set(10006,0);
byte DI7 = digitalRead(7);
if (DI7 >= 1)regBank.set(10007,1);
if (DI7 <= 0)regBank.set(10007,0);
//Digital output
int DO8 = regBank.get(8);
if (DO8 <= 0 && digitalRead(8) == HIGH)digitalWrite(8,LOW);
if (DO8 >= 1 && digitalRead(8) == LOW)digitalWrite(8,HIGH);
int DO9 = regBank.get(9);
if (DO9 <= 0 && digitalRead(9) == HIGH)digitalWrite(9,LOW);
if (DO9 >= 1 && digitalRead(9) == LOW)digitalWrite(9,HIGH);
int DO12 = regBank.get(12);
if (DO12 <= 0 && digitalRead(12) == HIGH)digitalWrite(12,LOW);
if (DO12 >= 1 && digitalRead(12) == LOW)digitalWrite(12,HIGH);
int DO13 = regBank.get(13);
if (DO13 <= 0 && digitalRead(13) == HIGH)digitalWrite(13,LOW);
if (DO13 >= 1 && digitalRead(13) == LOW)digitalWrite(13,HIGH);
//Analog input ***READ Twice deliberately
AI0 = analogRead(0);
delay(10);
AI0 = analogRead(0);
regBank.set(30001, (word) AI0);
delay(10);
AI1 = analogRead(1);
delay(10);
AI1 = analogRead(1);
regBank.set(30002, (word) AI1);
delay(10);
AI2 = analogRead(2);
delay(10);
AI2 = analogRead(2);
regBank.set(30003, (word) AI2);
delay(10);
AI3 = analogRead(3);
delay(10);
AI3 = analogRead(3);
regBank.set(30004, (word) AI3);
delay(10);
AI4 = analogRead(4);
delay(10);
AI4 = analogRead(4);
regBank.set(30005, (word) AI4);
delay(10);
AI5 = analogRead(5);
delay(10);
AI5 = analogRead(5);
regBank.set(30006, (word) AI5);
delay(10);
//Analog output
word AO10 = regBank.get(40010);
analogWrite(10,AO10);
delay(10);
word AO11 = regBank.get(40011);
analogWrite(11,AO11);
delay(10);
slave.run();
}
}
