modem lights
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 - If you have an external modem, those flashing or steady lights tell you what's happening in the ongoing "handshaking" or interaction between a computer (with its Universal Asynchronous Receiver/Transmitter or UART microchip) and the modem. Or, more formally, to use the RS-232C serial standard terms, between the Data Terminal Equipment (DTE) interface and the Data Communication Equipment (DCE) interface.| Modem Light | Meaning |
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| AA (auto answer) | The modem is ready to respond to an incoming call (assuming a communication program is also ready to handle the call). Since this light can be off even when the modem is ready, it's not useful. | | CD (carrier detect) | This simply indicates that the computer and the modem have recognized each other and that a carrier connection is established. If a second call is received, carrier detect may be temporarily interrupted and, depending on a number of factors, the first connection may be dropped or lost. | | HS (high speed) | If on, indicates that the modem is ready to transfer data at its highest speed. Since this is often the case, this light is also not very useful. | | MR (modem ready) | If on, indicates that your modem is ready to operate. | | OH (off hook) | If on, tells you that the phone line is ready for use. | | RD (receive data) | When flashing on, indicates that the modem is receiving data or signals from a remote computer. | | SD (send data) | When flashing on, indicates that the modem is sending data or signals to another computer. | | TR (terminal ready) | When on, indicates that your computer's communications program is active. If it's not on, either the program or your computer may not be working. |
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| CONTRIBUTORS: |
Paul Ruffolo |
| LAST UPDATED: |
07 Aug 2006
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