Hello rudolf48,
This...
The application program must have the following statements for debug output, for example:
# declaration
#include <TinyDebugSerial.h>
TinyDebugSerial mySerial = TinyDebugSerial(); // PB1 = TX pin
in function setup()
mySerial.begin( 9600 ); // for tiny_debug_serial
in function loop()
mySerial.println( "Testing..."); // debug output
...is not necessary. The Tiny Core already includes an instance of TinyDebugSerial named Serial. This should work...
# in function setup()
Serial.begin( 9600 ); // for tiny_debug_serial
# in function loop()
Serial.println( "Testing..."); // debug output