AT command set
The AT command set is a set of commands originally developed by Hayes Microcomputer Products that have become the industry standard for configuring and parameterizing modems . The characters “AT” stand for “attention” and must be sent before each command. By measuring the length of the individual bits, the transmission speed of the interface is determined automatically.
The first modem with this instruction set was sold by Hayes in 1981 under the name Smartmodem .
A device that can handle the AT command set is also referred to as Hayes-compatible . This instruction set was partially implemented by the ITU-T in Recommendation V.25ter; today's name is V.250. The use of this standard makes the use of device-specific modem drivers superfluous in practice.
Under Windows up to version 3.x, a native standard driver of the operating system is used, which controls the modem using the AT command set. Since Windows 95 , device-specific device drivers can also be used for modems, so that "Hayes compatibility" is no longer absolutely necessary under Windows and therefore does not have to be implemented in some modems. However, this can make it difficult to use these non-Hayes-compatible devices with other operating systems or even exclude them with other modems if no special drivers are available.
Classes
The AT command set is divided into four classes:
- basic command set
- This set contains the basic commands such as B. Replace the handset, adjust the volume. The commands consist of the character string AT followed by a letter and possibly subsequent digits. Upper / lower case is not important, since these characters in ASCII only differ in one bit and this bit is ignored.
- Example: ATD1234 means: Warning ( At tention) (select D ial) the number 1234th
- extended or enhanced command set
- This is the extended command set (hardware-related settings, such as modem test or data compression). The commands consist of an AT &, AT +, AT% or AT * followed by a letter and possibly a number.
- special command set
- Special orders
- register command set
- Commands that act directly on the register set .
- ATS2? supplies the value from register 2
- ATS2 = 6 assigns the value 6 to register 2
Web links
- V.250 standard publication by the ITU (English)
- http://www.xs4all.nl/~itsme/projects/phones/thuraya-hcs-7100-at-commands.html (also contains information on the AT commands supported by cell phones)
- http://www.nobbi.com/atgsm.html (AT command overview for cell phones)
- TS 27.007 Specification published by the 3GPP