INT 14h,  03h (3)        Get Serial Port Status

Returns line status and modem status information for a specified
serial port.

On entry:      AH         03h
DX         Serial port number (0 - COM1, 1 - COM2, etc.)

Returns:       AX         Line and Modem status (See below)

                                                                          

Status information is returned in AX, as follows:

 AH (Line status)
7 6 5 4 3 2 1 0
1 . . . . . . .       Time-out error
. 1 . . . . . .       Transfer shift register empty
. . 1 . . . . .       Transfer holding register empty
. . . 1 . . . .       Break-detect error
. . . . 1 . . .       Framing error
. . . . . 1 . .       Parity error
. . . . . . 1 .       Overrun error
. . . . . . . 1       Data ready

 AL (Modem status)
7 6 5 4 3 2 1 0
1 . . . . . . .       Received line signal detect
. 1 . . . . . .       Ring indicator
. . 1 . . . . .       Data set ready
. . . 1 . . . .       Clear to send
. . . . 1 . . .       Change in receive line signal detected
. . . . . 1 . .       Trailing edge ring detector
. . . . . . 1 .       Change in data set ready
. . . . . . . 1       Change in clear to send

If bit 7 of the Line status byte (AH) is set, then the rest of the
bits in AH and AL are unpredictable.


Notes:         Early versions of the ROM-BIOS for the original PC
had a programming error that would cause "time-out"
errors to be reported as "transfer shift register
empty" and "break-detect" errors. This has been
corrected in all other versions of the ROM-BIOS.


INT 14h, 03h (3) Get Serial Port Status