The following acronyms are used with the display lights on an external modem to identify the unit's current status. For some functions, there is more than one acronym that can be used.

   Acronym  Meaning
   AA       Auto answer mode
   CA       Compression active
   CD       Carrier detect
   CTR      Clear to receive
   CTS      Clear to send
   DTR      Data terminal ready (terminal ready)
   EC       Error control active
   HS       High speed (typically 4,800 bps and up)
   LB       Low battery
   MR       Modem ready (data set ready)
   OH       Off hook
   PWR      Power on
   RI       Ringing
   RNG      Ringing
   RTS      Request to send
   RXD      Receiving data
   RD       Receiving data
   SD       Transmitting (sending) data
   TD       Transmitting (sending) data
   TXD      Transmitting (sending) data
   TM       Test mode
   TR       Terminal ready