| Abbreviation | Name | Description |
| MR | Modem ready | On when power is applied to modem |
| TR | Terminal ready | The modem/computer is ready to receive and transmit commands. DTR signal is active. |
| SD/TX | Transmit data | Indicates that the modem is transmitting data. |
| RD/RX | Receive data | Indicates that the modem is receiving data. |
| OH | Off Hook | On when the modem is off-hook (picked up a line) |
| CD | Carrier detect | Remote carrier has been detected. |
| AA | Auto Answer | Flashes when ring is detected or when auto answer is enabled. |
| CS | Clear to send | Modem is ready to receive more data. |
| HS | High Speed | The established connection is above a certain bps speed (varies with different modems ). |
| EC | Error correction | Modem is performing error correction. |
