hi @ofTheo , take a look at the [whole function](https://github.com/openframeworks/openFrameworks/blob/develop/libs/openFrameworks/communication/ofSerial.cpp#L518-L560), it's hard to tell what the logic is : )

if the port is not inited it returns bool false.
if there's some error while writing, it returns OF_SERIAL_ERROR, which is -1 (which is bool true).
if there's no error and it writes 1 byte it returns 1 (which is also bool true).

basically, it returns true if there's a write error, or if it successfully wrote 1 byte. 

there are 2 ways to fix this, but since the error checking is bugged anyway I think it could be changed to be more consistent with ```ofSerial::writeBytes(...)``` .