From Xojo Documentation
| This item was deprecated in version 2019r2.
Please use SerialConnection.XON as a replacement.
Property (As Boolean )
Enables XON flow control.
|Changing property values does not automatically change the state of the hardware, you must call Reset or re-Open the connection in order for the change to take effect.|
This example enables XON flow control.
Serial1.XON = True