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)