The WM_COMMNOTIFY message is posted by a communication device driver whenever a COM port event occurs. The message indicates the status of a window's input or output queue.
wParam
Specifies the identifier of the communication device that is posting the notification message.
lParam
Specifies the notification status in the low-order word. The high-order word is zero. The notification status may be one or more of the following values:
| Value | Meaning |
| ReceiveTrigger | Indicates that at least wInTrigger bytes are in the input queue. wTrigger is a parameter of the EnableCommNotification function. |
| ReceiveTimeout | Indicates that at least one byte is in the input queue, but no more were received before the timeout period expired. |
| TransmitTrigger | Indicates that fewer than wOutTrigger bytes are in the output queue waiting to be transmitted. wOutTrigger is a parameter of the EnableCommNotification function. |
An application should return zero if it processes this message.