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What are AT Commands? Introducing Hayes Command Modem Control and Communication Settings
AT commands, an abbreviation for Attention commands, are a set of instructions used to control and configure modems and other communication devices. Initially introduced by the Hayes Microcomputer Products company in the late 1970s, AT commands have since become a widely accepted standard for modem communication.
The primary function of AT commands is to establish communication between a controlling device, such as a computer, and a modem. These commands allow the controlling device to send instructions and retrieve important information from the modem. The commands are transmitted as a series of characters, often starting with the prefix “AT” followed by a specific command and its parameters.
Hayes Command Set
The Hayes Command Set, also known as the Hayes AT Command Set, is an early and influential implementation of AT commands. The Hayes Command Set was developed by Hayes Microcomputer Products for their Smartmodem series of modems. It introduced a standardized way to control the modem, enabling features such as dialing, answering calls, diagnostics, and even basic file transfer.
One of the defining characteristics of the Hayes Command Set is the use of the “AT” prefix before each command. For example, “ATDT” is used to dial a telephone number, “ATA” to answer an incoming call, and “ATZ” to reset the modem to its default settings.
Modem Control and Communication Settings
AT commands provide a wide range of functionalities to control and configure modems. They can be used to adjust parameters such as baud rate, flow control, and error correction, ensuring optimal communication between devices. Here are a few common AT commands related to communication settings:
- AT+IPR: This command sets the baud rate for communication between the modem and the controlling device. For example, “AT+IPR=9600” sets the baud rate to 9600 bits per second.
- AT&F: This command restores the modem’s factory default settings.
- AT&C: This command controls the carrier detect (DCD) signal, which indicates the presence of a carrier (phone line connection).
- AT&D: This command controls the data terminal ready (DTR) signal, which indicates whether the modem is ready to communicate with the controlling device.
- ATX: This command controls the flow control method used during data transmission.
By using AT commands, developers and users can configure their modems to meet specific communication requirements. These commands have played a crucial role in the evolution of modem technology, providing a standardized and efficient way to control and communicate with these devices.
It is worth noting that although the original Hayes Command Set is widely used, there are now numerous variations and extensions to the AT command set standardized by the International Telecommunication Union (ITU) under the V.25ter recommendation.
So next time you encounter a modem or any communication device that supports AT commands, remember that these simple and powerful instructions are the backbone of their control and configuration, enabling seamless and efficient communication.
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