INT 14h,  02h (2)        Receive One Character

    Receives one character at the specified serial port.

       On entry:      AH         02h
                      DX         Serial port number (0 - COM1, 1 - COM2, etc.)

       Returns:       AL         Character
                      AH         Line status (See service 03h)

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       Notes:         This service waits for a character. If no character
                      is available or an error occurs, no character is
                      returned and bit 7 of AH is set.

                      If an error occurs, bit 7 of AH is set. Since bit 7
                      is used as a general error flag, this service is
                      unable to identify a time-out error. For complete
                      diagnostic information, use Service 03h (Get serial
                      port status).