When connecting to a Linux device using a serial port there may be times where that connection becomes stuck open and thus will not provide sane output to the TTY port. This issue can be resolved by killing the PID (Process ID) and letting the serial port process restart.
The serial port connection should be configured in inittab which will allow you to specify various configuration options as well as respawning the process. So when you specify respawn the process will automatically restart if it is no longer running as will be the case if you kill the process off. The inittab entry will look similar to one of the two below examples.