Boxes before 0 in serial monitor

shantanu0121kumar · May 12, 2023, 4:28am

Why are there boxes before the 0 on the serial monitor?

ptillisch · May 12, 2023, 4:37am

Hi @shantanu0121kumar. The Arduino IDE developers are tracking this bug here:

github.com/arduino/arduino-ide

Spurious output in Serial Monitor after upload

opened 08:23AM - 24 Mar 22 UTC

per1234

topic: code type: imperfection topic: CLI topic: serial monitor criticality: low

### Describe the problem The first output printed to Serial Monitor after an …upload is some "garbage" characters. ![image](https://user-images.githubusercontent.com/8572152/159872636-d8e0c920-e628-4c91-9c91-65611fcfcaaa.png) ### To reproduce #### Equipment - Arduino board that uses the ATmega16U2 USB chip: - Arduino Uno - Arduino Uno Mini - Arduino Mega #### Steps 1. Upload a sketch to your board that prints to `Serial`: ```cpp void setup() { Serial.begin(9600); Serial.println("hello world"); } void loop() {} ``` 1. Open the "**Serial Monitor**" view. 🐛 The output starts with some unexpected content: ```text □□□□□□□□□□□hello world ``` ### Expected behavior Serial monitor output always reflects the data sent by the board. ### Arduino IDE version 2.0.0-rc5-snapshot-4de7737 ### Operating system Windows ### Operating system version 10 ### Additional context The number of `□` in the demonstration matches the number of characters that are printed by the sketch. --- The spurious output does not occur when the output is triggered by resetting the board, so it is specific to the upload operation. --- The spurious output still occurs even if you add a delay before the print, so it is not a matter of timing from initialization as is sometimes the cause of corrupted serial output. --- The issue does not occur when using Arduino IDE 1.x --- I have only been able to reproduce this issue with the Arduino boards that use an ATmega16U2 USB to serial adapter chip. I could not reproduce it when using boards with other USB interfaces: - Native USB (Leonardo, Nano 33 IoT) - FTDI FT232R (Nano, Pro Mini) - WCH CH340 (3rd party boards) --- Originally reported at https://forum.arduino.cc/t/serial-monitor-contains-garbage-after-upload/972312 #### Additional reports - https://forum.arduino.cc/t/serial-monitor-confusion/1111552 - https://forum.arduino.cc/t/serial-monitor-prints-boxes-when-opened/1102169 - https://forum.arduino.cc/t/boxes-before-0-in-serial-monitor/1126046 ### Issue checklist - [X] I searched for previous reports in [the issue tracker](https://github.com/arduino/arduino-ide/issues?q=) - [X] I verified the problem still occurs when using the latest [nightly build](https://github.com/arduino/arduino-ide#nightly-builds) - [X] My report contains all necessary details

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Boxes before 0 in serial monitor

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