Arduino Pro Mini ATmega 328P 3.3V 8MHz, connected to USB port via USB to Serial breakout board built around the FT232RL FTDI chip. JTAGenum project code uploaded to the Arduino. I opened terminal and tried to run test command (without connecting wires between target and Arduino), but terminal output show garbage values. The baud rate of the serial console has been set 115200, as specified in JTAGenum code. Not sure whether this issue can be related to CPU_PRESCALE defintions in code.

  • 1
    Most likely an incorrect F_CPU. Do you have the right board selected in the IDE?
    – Majenko
    Oct 15, 2017 at 22:38
  • Do sketchs loads OK? Only serial monitor is not OK?
    – user31481
    Oct 15, 2017 at 22:52
  • I managed to upload sketch. I use Arduino Web Editor, I selected 'Board as Arduino Pro or Pro Mini', first it show red cross(disconnected) state, when click Change on menu, it stay connected, but when I check board type I noticed that FLAVOUR by default always selected '16MHz ATmega328', not '8MHz ATmega328'. When I select '8MHz ATmega328' it show disconnected state, so I should press Change. Does this mean my OEM board is 16MHz, not 8MHz?
    – minto
    Oct 15, 2017 at 23:39
  • The IDE cannot know what your board is - that is down to you to tell it. If it's an 8MHz board and you tell the IDE 16MHz you will get garbage. If its a 16MHz board and you tell the IDE 8MHz you will get garbage. If you don't know which you bought, why did you buy it?
    – Majenko
    Oct 16, 2017 at 9:38
  • No. I think Arduino Web Editor (as part of Arduino IDE) capable automatically detect the kind of board and the port it is connected to without having to individually select them. That's why Arduino Web Editor by default always show '16MHz ATmega328' in FLAVOUR menu. But in my Pro Mini ATmega board description was stated its 328P 3.3V 8Mhz model.
    – minto
    Oct 16, 2017 at 12:53

1 Answer 1


Garbage values on output is mostly due to the baudrate.

  1. Try changing the baudrate on the output terminal to the baudrate in the code.
  2. Try checking the output by changing different baudrates on the terminal.

This must work for you :)

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.