I send a variable using a programming language to COM serial port. I have a condition if(incomingByte != 0) that is satisfied if I send something to the serial port using the mentioned PL. However, due to serial ports concurrency, I cannot see what's received at that exact moment.
However, when I don't send anything, I open Serial Monitor and output the read variable thanks to command Serial.read(), I always receive 0.
From the documentation, we can read that serial read returns "-1 if no data is available".
int incomingByte = 0; // for incoming serial data
void setup() {
Serial.begin(9600); // opens serial port, sets data rate to 9600 bps
pinMode(13, OUTPUT);
}
void loop() {
int inverse;
// send data only when you receive data:
if (Serial.available() > 0) {
char incomingByte = (char)Serial.read();
// Serial.write(Serial.read());
// inverse = incomingByte;
}
if(incomingByte == '1'){
digitalWrite(13, HIGH);
}
else if(incomingByte == '0'){
digitalWrite(13, LOW);
}
// say what you got:
Serial.print("I received: ");
Serial.println((char)incomingByte, HEX);
}
Here you declare a global variable named incomingByte:
int incomingByte = 0; // for incoming serial data
Here you declare a variable local to the if block named incomingByte:
char incomingByte = (char)Serial.read();
that variable goes out of scope at the end of the if block.
Here you print the value of the global variable named incomingByte:
Serial.println((char)incomingByte, HEX);
The Arduino language allows you to declare multiple variables of the same name at different scopes. This is called "variable shadowing", and is the cause of a lot of confusion.
You need to understand the difference between a variable declaration:
char incomingByte = (char)Serial.read();
and a variable definition:
incomingByte = (char)Serial.read();
A declaration creates a new variable. A definition assigns a value to an existing variable.
int incomingByte; // for incoming serial data
void setup() {
Serial.begin(9600); // opens serial port, sets data rate to 9600 bps
pinMode(13, OUTPUT);
}
void loop() {
if (Serial.available() > 0)
incomingByte = Serial.read();
if(incomingByte != 0){
digitalWrite(13, HIGH);
}
else if(incomingByte == 0){
digitalWrite(13, LOW);
delay(1000);
digitalWrite(13, HIGH);
}
Serial.println(incomingByte, DEC);
}
If I send anything from the PL to the Arduino through COM (32-bit LongInt), the condition if(incomingByte != 0) is satisfied and the led lights. When I open Serial Monitor in Arduino IDE, the second condition else if is satisfied and led starts blinking (even though I am not anymore sending anything, I receive tons of 0's, while the expected result should be -1).
P.S.:
*** The real problem behind this that I am trying to solve is reading correctly a 32-bit Long Integer that I send from the PL. The only thing Arduino understands is !=0, and I would like it to recognize the 0 as well, so I can turn off the Led. As I can't see the values I receive, I can really debug the code, or even know the origin of the problem. I know that INT in Arduino is only 16 bits and that encoding of the data types must not necessarily coincide. How should I refine the variable in the PL before sending it to Arduino, so it is interpreted correctly?? ***
mahdibk:
When I open Serial Monitor in Arduino IDE, the second condition else if is satisfied and led starts blinking (even though I am not anymore sending anything, I receive tons of 0's, while the expected result should be -1).
When you open Serial Monitor the Arduino board is reset.
As incomingByte is then reinitialized to 0, the second condition else if(incomingByte == 0){ is satisfied.
mahdibk:
If I send anything from the PL to the Arduino through COM (32-bit LongInt), the condition if(incomingByte != 0) is satisfied and the led lights. When I open Serial Monitor in Arduino IDE, the second condition else if is satisfied and led starts blinking (even though I am not anymore sending anything, I receive tons of 0's, while the expected result should be -1).
You are not receiving tons of 0's. You are not receiving anything. Since you are not receiving anything, the global variable 'incominByte' is not being changed from its default value: 0. Every time you look the value it is still 0. Did you only want to process each incoming byte once? If so:
