INT 14 - SERIAL - GET PORT STATUS
        AH = 03h
        AL = 00h (ArtiCom)
        DX = port number (00h-03h) (04h-43h for Digiboard XAPCM232.SYS)
Return: AH = line status (see below)
        AL = modem status (see below)
        AX = 9E00h if disconnected (ArtiCom)
Note:   the 04/08/93 Compaq system ROM uses only the low two bits of DX
SeeAlso: AH=00h,AH=07h"MultiDOS",AX=8000h"ARTICOM",AH=81h"COURIERS",AX=FD02h

Bitfields for line status:
 bit 7  timeout
 bit 6  transmit shift register empty
 bit 5  transmit holding register empty
 bit 4  break detected
 bit 3  framing error
 bit 2  parity error
 bit 1  overrun error
 bit 0  receive data ready

Bitfields for modem status:
 bit 7  carrier detect
 bit 6  ring indicator
 bit 5  data set ready
 bit 4  clear to send
 bit 3  delta carrier detect
 bit 2  trailing edge of ring indicator
 bit 1  delta data set ready
 bit 0  delta clear to send

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