INT 14,2 - Receive Character from Communications Port

AH = 02

DX = zero based serial port number (0-1) (0-3 for AT)

on return:

AH = port status (see ~INT 14,STATUS~)

bit 7 = 0 if successful

bit 7 = 1 if call failed

AL = character received if call was success

- ~INT 14,3~ should be used to determine the actual cause of

the error since the time-out bit of the status register is

always set during an error on this call

- uses hardware flow control