Why the need for AT commands?

The AT commands to control modems. In fact, this string of characters that begin with the letters at and end with a carriage return. However, in the initialization string, the closing elements are automatically generated. The symbols AT commands can be either uppercase or lowercase. Between the individual commands can be placed in the blanks.

More features

In addition to the basic steps associated with the switching of the modem, AT commands can control S-registers the communication device. They contain a variety of service information that is necessary to ensure the functionality of the modem. For example, in S-register can be stored for constants that define the waiting time, types of used protocols, analog signals, the levels of input and output signals and so on. The number of registers determines the developer of the modem, sometimes their total number is several hundred. However it is accepted that the first of 13 such nodes maintain the purpose specified by the manufacturer. Despite the fact that the contents of S-register each user can modify and read at your own discretion, we should not forget that between the data in different nodes of the system has a very complex relationship. So an arbitrary change in any of the registers may lead to the fact that in the future it will be impossible to use a standard program for work on the Internet.

Basic AT commands that are most often used in modems

1. L0-L3 – indicates the speaker volume. The values correspond to minimum, low, medium, and maximum level.

2. In – means the request for data from the permanent storage device of the modem, where n corresponds to the number of the first team.

3. M0-M3 – the state dynamics, where:

- 0 - off device;

- 1 speaker is included from “hook” to the time when connection is established;

- 2 - the device is always off;

- 3 – speaker turns on only after pressing the last digit in the number, and turned off after establishing the communication session.

4. P and T – complies with the use of pulsed (PULSE) and tonal (TONE) dial.

5. S – work with the registers of the modem. SO? relevant site content SO. SO=1 means the assignment of the status register unit.

6. Z – means that the contents of all nodes is set to the initial level.

7. &F – complies with the recovery of information in the S-registers of the modem from the permanent storage device. This data is written by the manufacturer of the modem, they can't be changed by the user.

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8. &W – means to write the contents of all registers in a special non-volatile memory to maintain user settings.

AT commands for GSM modems

According to the GSM 07.07, line management team to define “context” is obliged to have the following form: +CGDCONT=[[,<PDP_type>[,[,<PDP_addr>[,<d_comp>[,<h_comp>[,[,…[,pdN]]]]]]]]]. Let us consider what means such a record (AT command):

1. cid – context ID. Always integer "+". The maximum value of it is determined by the model.

2. PDP_type - indicates the type of Protocol.

3. APN - name of access point is set by the operator.

4. d_comp – means the PDP data compression 0-off, 1-enabled.

5. h_comp corresponds to PDP header compression 0-off, 1-enabled.

6. pd1 ... pdN - involves string parameters specific to this type of Protocol.