I am a novice to Arduino. I came across an article on rs 485 and currently trying to implement the same between 2 arduino unos. I copied code from internet which is pretty simple but I am unable to make communication work properly. Here is the code for master arduino with explanation of what I am trying to do.
**Master Arduino Code**
/* master will send a message I1LF where I shows start of master message by master.
* 1 shows the slave device No. from whom data is to be fetched and L
* shows that master wants to read slave's sensor data
* and F indicates finish of message by master.
* slave will respond by sending Serial.println(i1) where i is slave no and 1 is to let master know that
* correct slave is sending data. then slave would send sensor_value and then f indicates end of slave message.
* master will display data read from rs 485 bus.
*/
#include<LiquidCrystal.h> //Library for LCD display function
LiquidCrystal lcd(4, 5, 6, 7, 8, 9);
const int Enable = 2;
int value1=0;
void setup()
{
Serial.begin(9600);
pinMode(Enable, OUTPUT);
digitalWrite(Enable, HIGH); // put master arduino into transmission mode.
lcd.begin(16,2);
lcd.clear();
}
void loop()
{
Serial.print('I'); // I indicates master has started communication.
Serial.print('1'); // this is the address of slave from whom data is to be fetched.
Serial.print('L'); // this means master wants to read sensor data.
Serial.print('F'); // this means end of message.
Serial.flush(); // wiat untill all data has been pushed to the serial.
digitalWrite(Enable, LOW); // put master into receiving mode.
if(Serial.find('i')) // i will be sent (to indicate start of slave message) by the slave that was
// prompted by master to answer.
{ // indicating master wants to read slave's sensor data.
int slave1 = Serial.parseInt(); // check which slave is sending data.
value1 = Serial.parseInt();
if(Serial.read() == 'f' && slave1 == 1) // f indicates end of message sent by slave and 1
//is the address of the slave sent by
// the slave so that master can recognize which slave is this.
{
lcd.setCursor(0,0);
lcd.print("Slave 1: ");
lcd.setCursor(11,0);
lcd.print(value1);
}
}
digitalWrite(Enable, HIGH);
delay(300);
}
````Preformatted text`
Slave Code
#include<LiquidCrystal.h>
LiquidCrystal lcd(4, 5, 6, 7, 8, 9);
const int Enable = 2;
const int SlaveNumber = 1;
void setup()
{
Serial.begin(9600);
pinMode(Enable, OUTPUT);
digitalWrite(Enable, LOW); // initially put slave in receiving mode
pinMode(A0, INPUT);
lcd.begin(16,2);
lcd.clear();
}
void loop()
{
if(Serial.available())
{
if(Serial.read()=='I') // all slaves will detect I on rs 485 bus which means master has started commmunication.
{
int Slave = Serial.parseInt(); // read next character on rs 485 bus which would definitely be a digit
//indicating slave no to whom master wishes to communicate.
if(Slave == SlaveNumber) // check if master wants to commnucate with you.
{
char command = Serial.read(); // read next character in serial buffer which would be command L
delay(100);
if(command == 'L')
{
if(Serial.read()=='F') // if master's message has finished.
{
int AnalogValue = analogRead(0); // read sensor
digitalWrite(Enable, HIGH); // put slave in transmission mode.
Serial.print("i"); // i indicates start of slave message
Serial.println(SlaveNumber); // send slave no so that master can identify
//which slave he is receiving data from.
Serial.print(AnalogValue);
Serial.print("f"); // indicates end of message by the slave.
Serial.flush();
digitalWrite(Enable, LOW); // put slave in listening ( receivig ) mode
}
}
}
}
}
}
This is screen shot of proteous simulation showing Master unable to read slave1's sensor data
https://drive.google.com/file/d/1QDYk4NMfvtLyZ-UyQsluTd0WxQgf5Tiv/view?usp=sharing
I assessed that problem arose because of master and slave both being in transmission mode so I attached a not gate between master's enable pin and slave's enable pin and then master is working fine. but practically attaching a not gate wont be possible. that's why I want to know how to ensure that enable of both master and slave is not high simultaneously. I have tried a couple of strategies and introduced delays at different locations in the code but nothing seems to work. by hit and trial it starts to work sometimes but I want to know the correct way of doing so.
This is screen shot of proteous simulation which shows master reading correctly slave1 data only after I attach a not gate between master Enable pin and Slave's Enable pin.
Code for both master and slave and circuit is exactly the same as before. only a not gate has been used between master's enable pin and slave's enable pin.
[proteous circuit of rs 485 working ](https://drive.google.com/file/d/1L1NsiTzgcBSSYoXa8uVOMnY0Uhg5vBDQ/view?usp=sharing)
