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User at modem A issues a dial command: AT-Get the modem's ATtention; D-Dial; T-Touch-Tone; 12125550100-Call this number RING: Modem A begins dialing. Modem B's phone-line rings, and the modem reports the fact. ATA: Computer at modem B issues answer command. CONNECT: CONNECT: The modems connect, and both modems report "connect".
The modem uses the Data Carrier Detect (DCD) pin to signal whether it's connected to a host. The computer can generally just read the DCD pin at any time and always know if the modem is in command or data mode. DCD high means data mode, and low means command mode. DCD is a signal sent from the modem to the computer.
The calling modem waits for the tone after it dials the phone line before it initiates data transmission. If it does not receive a carrier tone within a set amount of time, it will disconnect the phone line and issues the NO CARRIER message. The actual data is transmitted from the answering modem to the calling modem via modulation of the carrier.
During the POST, the BIOS must integrate multiple competing, changing, and even mutually exclusive standards and initiatives for the matrix of hardware and operating systems the PC is expected to support, although at most only simple memory tests and the setup screen are displayed.
It is not asserted until the modem either makes an outgoing call, or answers an incoming call, and then connects with a data modem on the other end. The signal is asserted at the same time the modem reports its CONNECT message, and stays asserted until the call is disconnected (either intentionally or because of a fault in the line).
Two POST seven-segment displays ("Q_CODE1" and "Q_CODE2", lower-left), integrated on a computer motherboard. Diagnostic cards are today mainly used by designers of motherboards and extension cards, along with logic analyzers and other debug tools and interfaces.
If something is wrong with your mobile web browser, it can cause AOL websites to stop working. Get back to what you're doing by fixing the source of the problem.
When the modem wants to tell the host about these, it sends a DLE byte, plus a (usually) 1-byte message describing the event. The list of supported events varies by modem, but usually a digit (as well as * and #) mean touch-tones pressed, and the letter "s" means silence detected.