The modbus RTU library for Android is available in two versions, debug and release. The first one is thought to be used in situations where you need to know more about which data the library is receiving and sending behind the scenes, whereas the release version has been designed for production.

In many occasions, the software development process involves to cycle iteratively between implementation and testing/validation of the application before release it. In these phases, the more information you know about the behavior of the system, the fast you will figure out a hypothetical issue.

The Android environment let you list all the debug strings by typing from the command line:

./adb logcat

in a Linux environment, the adb program is usually located in $ANDROID_SDK_PATH/platform-tools/. The same information is available for instance in the Eclipse IDE, under the DDMS perspective).

Release version does not display any information about the data read or written from/to the serial port. Indeed, any errors that might happen are not added to the log stream.