BIOS Asynchronous Communications Services (Status)

�7�6�5�4�3�2�1�0� AL modem status

� � � � � � � +---- clear to send status changed

� � � � � � +----- data set ready status changed

� � � � � +------ trailing edge ring indicator

� � � � +------- receive line signal changed

� � � +-------- clear to send

� � +--------- data set ready

� +---------- ring indicator

+----------- receive line signal detected

�7�6�5�4�3�2�1�0� AH port status

� � � � � � � +---- data ready

� � � � � � +----- overrun error

� � � � � +------ parity error

� � � � +------- framing error

� � � +-------- break detect

� � +--------- transmit holding register empty

� +---------- transmit shift register empty

+----------- time out (N/A for functions 1 and 2)