Int 14H [PC] [AT] [PS/2] Function 03H Get communications port status

Returns the status of the specified serial communications port.

Call with:

AH = 03H

DX = communications port number (0 = COM1, 1 = COM2, etc.)

Returns:

AH = port status (see Int 14H Function 00H)

AL = modem status (see Int 14H Function 00H)