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Decoding the Mystery of Serial.clear() in Arduino



Arduino's serial communication is a powerful tool for debugging, interacting with external devices, and displaying data. However, managing the serial monitor output can become messy if not handled properly. This article simplifies the often-misunderstood `Serial.clear()` function and demonstrates its practical applications. We'll demystify its functionality, showing you when and why you'd use it.

Understanding Serial Communication in Arduino



Before diving into `Serial.clear()`, let's review the basics. Arduino uses serial communication to send and receive data through a digital pin (typically pins 0 and 1). Data is transmitted serially, one bit at a time. The `Serial.begin(baudRate)` function initializes the serial port, specifying the baud rate (data transmission speed, usually 9600). Functions like `Serial.print()` and `Serial.println()` send data to the serial port, which can then be viewed using the Arduino IDE's Serial Monitor.

This data remains in the serial buffer until it's read by the Serial Monitor or other receiving device. This buffer acts as a temporary storage area, holding data waiting to be sent or received. A large amount of unsent data in the buffer can lead to unexpected behavior and data loss. This is where `Serial.clear()` comes in handy.

What is Serial.clear()?



`Serial.clear()` is a function that flushes the serial input buffer. It doesn't directly affect the output buffer. In simpler terms, it empties the queue of data waiting to be read from the serial port. Any data already sent to the serial port (using `Serial.print()`, etc.) remains unaffected. This function is crucial for preventing lingering data from interfering with subsequent communication.

Important Note: `Serial.clear()` only clears the input buffer. It does not clear the output buffer. The output buffer holds data waiting to be transmitted. To clear the output buffer, you'd need to wait until all data is sent (which might involve delaying your program execution).


When to Use Serial.clear()?



`Serial.clear()` is particularly beneficial in scenarios where you need to ensure you're working with fresh data. Here are some key situations:

Beginning a new communication sequence: Imagine a program that waits for a specific command from the serial monitor. If previous commands are still lingering in the input buffer, they might be misinterpreted. `Serial.clear()` at the start ensures you receive only the intended command.

Handling user input: If your program takes user input through the serial monitor, clearing the buffer before requesting input prevents accidental use of previous input data.

Error handling and recovery: If an error occurs during serial communication, leftover data in the buffer might prevent the program from recovering smoothly. Clearing the buffer can assist in restarting the communication process.

Interfacing with other devices: When communicating with other devices via serial, clearing the buffer before sending a new command guarantees the device receives only the current instruction.


Practical Examples



Example 1: Clearing the buffer before receiving a command:

```arduino
void setup() {
Serial.begin(9600);
}

void loop() {
Serial.println("Enter a command (start/stop):");
Serial.clear(); // Clear the input buffer before reading the command
if (Serial.available() > 0) {
String command = Serial.readStringUntil('\n');
// Process the command
}
}
```

Example 2: Clearing the buffer after an error:

```arduino
void setup() {
Serial.begin(9600);
}

void loop() {
// ... some code that might cause a serial communication error ...
if (errorOccurred) {
Serial.println("Error occurred. Clearing buffer.");
Serial.clear();
// Attempt to re-establish communication
}
}
```


Key Takeaways



`Serial.clear()` is a powerful yet simple function that can significantly improve the reliability and predictability of your Arduino serial communication. By strategically using `Serial.clear()` to manage the input buffer, you can prevent data corruption, unexpected behavior, and enhance the overall performance of your applications. Remember, it only affects the input buffer, leaving the output buffer untouched.


FAQs



1. Does `Serial.clear()` affect data already sent to the serial monitor? No, it only clears the input buffer. Data already sent via `Serial.print()` remains unaffected.

2. Can I use `Serial.clear()` repeatedly without any negative consequences? Yes, it's safe to call `Serial.clear()` multiple times. It simply clears the input buffer; there's no inherent limit to how often it can be used.

3. What happens if I don't use `Serial.clear()`? Lingering data in the input buffer might lead to unexpected behavior, data misinterpretations, and communication errors.

4. Is there a way to clear the output buffer? There's no direct function to clear the output buffer. You need to ensure all data has been transmitted (using delays or flow control mechanisms).

5. Why is my serial monitor still showing old data after calling `Serial.clear()`? Make sure you're using `Serial.clear()` before you try to receive new data. Also, check your baud rate setting in both the Arduino code and the Serial Monitor to ensure they match. Inconsistencies here can lead to communication issues.

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Please add a new command Serial.clear() - Arduino Forum 21 Jun 2022 · Hi, Serial monitor has a 'Clear output' button. And why is there no such command from Arduino? For example: Serial.Clear(); (command: 'FF' code: 0C = 'form feed') This will allow you to observe a static inscription in several lines, as on the display without shifting them. Now you can output only one line by disabling NL&CR, but what if you need 10 lines? Best regards.

How to clear serial buffer? - Programming - Arduino Forum 28 Jun 2014 · How would I clear it though? with the serial flush? Assuming you are using a current version of Arduino IDE, Serial.flush () relates to sending data; it does not clear the receive buffer. +1 to steinie44's reply.

Clearing Arduino's serial buffer - Stack Overflow 12 Oct 2014 · but once i give 'a'. it starts glowing and never goes off. is it reading the char 'a' from the buffer? if so then how to clear it ? Serial.flush () not working. any ideas please. am new to arduino. sorry if its silly.

Clearing the data in Serial monitor - Arduino Forum 27 May 2019 · Hello, I am new to Arduino. I am stuck with clearing the serial monitor using serial commands of Arduino. Is it possible to clear the Serial monitors' data every time the void loop runs?

arduino - Clearing the terminal screen? - Stack Overflow 11 Apr 2012 · The Arduino serial monitor isn't a regular terminal so its not possible to clear the screen using standard terminal commands. I suggest using an actual terminal emulator, like Putty.

How do I clear the screen (cls) in the Serial Monitor? - Arduino … 10 Nov 2014 · If you use a "real" terminal emulator (minicom, putty, realterm, etc) instead of the Arduino IDE's built-in serial monitor, you will gain the ability to clear the screen (and do all sorts of other things) using "escape sequences."

Clearing the Serial Monitor screen - Arduino Forum 3 Jul 2012 · To clear the serial monitor, you have to modify the source code to let it be cleared. To do that, you must download the arduino source, apply the change I gave you, compile it, and then run it.

Clearing serial buffer solved - Education - Arduino Forum 18 Apr 2014 · Recall that the older arduino flushing function did clear the serial input buffer, but they changed it around IDE => 1.0 to flush only the output transmit buffer and left no function to clear the input buffer. If it was a useful or logical function …

Clear Screen on Serial Monitor. - Arduino Forum 23 Nov 2009 · To clear the screen in a terminal emulator, a standard clear screen command is (esc) [2J, so your code would look like this: Serial.print (27,BYTE); //Print "esc" Serial.print (" [2J"); This will not work in the Arduino Serial Monitor, so you need a terminal emulator. Since it doesn't use a serial port, you also need a serial port emulator.

How to clear the Serial buffer? - Programming - Arduino Forum 7 Feb 2016 · Which "Support" page are you looking at? arduino.cc Serial.flush () - Arduino Reference The Arduino programming language Reference, organized into Functions, Variable and Constant, and Structure keywords.