AT command set of AT command

AT is to noTE thAT at instruction set is sent from terminal equipment (te) or data terminal equipment (DTE) to terminal adapter (ta) or data circuit terminal equipment (DCE). AT commands are sent by TA and TE to control the functions of mobile station (MS) and interact with GSM network services. Users can control calls, short messages, phone books, data services, faxes, etc. through AT commands. In the early 1990s, the AT instruction was only used for modem operation. There is no precedent for controlling SMS, only a protocol called SMS BlockMode has been developed, which is completely controlled by terminal equipment (TE) or computer. A modem command language invented by Hayes Company has become a de facto standard and has been adopted by all modem manufacturers. Each command begins with the letter AT, hence the name. AT is followed by letters and numbers to indicate specific functions. Short message service. Later, the major mobile phone manufacturers Nokia, Ericsson, Motorola and Hewlett-Packard * * * developed a set of at instructions for GSM, including the control of short messages. On this basis, AT instruction evolved and added to GSM07.05 standard and GSM07.07 standard, which was completely standardized and relatively sound. For example, there are three ways to control SMS: initial BlockMode；; TextMode is based on AT instruction; PDUMode based on AT instruction. To PDUMode has replaced BlockMode and gradually faded out. The communication protocol between GSM module and computer is some AT instruction sets. The AT instruction is a string thAT starts with AT and ends with a character, and the response packet of the at instruction is in. Whether each instruction is executed successfully or not will be rewarded accordingly. For other unexpected information (such as someone dialing in, no signal on the line, etc.) ), the module will have some corresponding information prompts, and the receiving end can do corresponding processing. When the Internet first appeared, people used modems to connect. Modems are usually at both ends of the telephone line, and the modems start to connect and end the operation. Whether the modem is in "start" or "answer" mode, the caller usually switches his modem to "start" and then dials manually. When the remote modem answers, it should have been set to "Answer" mode, the handset is turned off, and communication continues until the caller disconnects manually.

When automation is needed, it usually only needs to be done at the answering end-for example, a bank may need to call in from a branch number to end its daily processing. In order to play this role, some modems have automatic off-hook function in answer mode and line clearing function when other users disconnect manually. There is little need for automatic dialing, which is handled by an independent peripheral "dialer". This is usually plugged into a separate input/output port on the computer (usually an RS-232 port) and requires the modem itself to be programmed separately.

This operation method was very effective in the 1960s and early 1970s, when modems were usually used to connect terminal devices such as computers (dialing out) or intelligent computer hosts (answering). However, the microcomputer revolution in the 1970s led to the introduction of low-cost modems and made the idea of semi-dedicated point-to-point connection no longer applicable. Thousands of potential users may have to dial any other thousands of users, and the only solution at that time was to let users dial manually.

The computer industry needs a way to tell the modem what number to dial through software. The early stand-alone dialer had this function, but it can only use a single port, and the microcomputer may not have it. Another solution is to use a single set of "command pins" to send and receive commands, and another set can use signal pins to indicate that the modem should interpret the received data as commands. These are all supported by the hardware in RS-232 standard. However, many implementations of RS-232 port of microcomputer are very basic. In order to save cost, many pins are cancelled. In 198 1 year, Hershey Communication introduced an intelligent modem solution, which can reuse the existing data pins without modification. In addition, the modem itself can switch between two modes:

1, the data mode when the modem sends data to the remote modem. In data mode, the modem sends any data it receives from the computer through the telephone line.

2, the data is interpreted as the command mode given to the local modem (the command that the local modem should execute).

When switching from data mode to command mode, the session issues an escape sequence string with three plus signs ("++++"), followed by a one-second pause. Pause after the escape sequence is necessary to reduce the problems caused by inbound signals: if any other data is received within 1 second after receiving three plus signs, it is not an escape sequence and will be sent as data. To switch back, they send an online command, o. In practice, many commands automatically switch to online mode after completion, but online commands are rarely used by users.

In order to avoid Hertz's patent authorization, some manufacturers have implemented escape sequences without time interval protection (TIES). There is a major impact here, which is denial of service security. When the computer tries to send the byte sequence "++ath0" in data mode, it will cause the modem to hang. For any computer connected to the Internet through this modem, this vulnerability can be easily exploited by sending a death request ping containing "++ath0" payload sequence. The computer operating system will automatically try to reply the sender with the ICMP payload, and the modem will interpret the payload data of the Internet control message protocol as a Hershey command, and immediately disconnect itself from the Internet. The same error may also be triggered, for example, a computer user tries to send an email containing the above string. He's command set includes various telephone line operation commands such as dialing and hanging up. It also includes various controls on modem settings, including a set of register instruction sets, allowing users to set various memory locations directly on the original Hershey modem. A considerable part of this instruction set was copied word for word by almost all early 300-baud modem manufacturers, including the meaning of registers.

The expansion of 1200 and 2400 baud requires a small set of new commands, some of which are prefixed with ("&") to show support for new functions. Heinz himself was forced to launch a 2400 baud model soon after their 1200. As a time-saving method, the command set was the same as that of 1200. Basically by accident, the users of the existing 1200 baud rate modem used the new HEMS2400 without changing the software, which strengthened the use of HEMS2400 version commands. A few years later, TIA/EIA took the 2400 baud rate command set as the official standard and named it: data transmission system and equipment-serial asynchronous automatic dialing and control, TIA/EIA-602.

However, Hershey's mobile communication has made slow progress in high-speed application or compression, while the other three companies have begun to lead -Microcom, U.S. Robotics and Telebit. These three companies use their own extended command set instead of waiting for Heinz. By the early 1990s, there were four main command sets in use, and some versions were based on one of them. In the early 1990s, with the widespread introduction of 14.4 and 28.8 kbit/s, things became simple again. Slowly, use "&"on the basis of the original command set. Extended command sets became popular and then became common. Only one other command set has been popular: the American robot modem command set. The following text lists some Hershey's command sets (also known as AT commands: AT stands for attention).

He's command can be divided into four groups:

1. Basic command set-a capital letter followed by a number. Such as: M 1.

2. Extended command set-a "&"(and symbol) and capital letters followed by a number. It is an extension of the basic command set. For example,&M 1. Note: m1and&; M 1 is different.

3. Proprietary command set-usually starts with a backslash ("\") or a percent sign ("%"); These commands vary greatly among different modem manufacturers.

4. Register command -Sr = n, where r is the register number to be changed and n is the new value to be allocated.

A register represents a specified location in memory. The modem has a small amount of memory on the motherboard. The purpose of the fourth set of commands is to input values into specific registers (memory locations). This register will store specific variables (alphanumeric information) that can be used by modems and communication software. For example, S7 = 60 instructs the computer to "set the value of register #7 to 60".

Although most commands of instruction set syntax are defined by alphanumeric combinations (L0, L 1, etc.). ), zero is optional. In this example, "L0" is equivalent to the ordinary "L". Please keep this in mind when reading the table below.

In data mode, the escape sequence can return the modem to command mode. The normal escape sequence is three plus signs ("++"). In order to distinguish it from possible real data, a pause must be added in front of it, and there is no pause between the plus signs, followed by a pause; The default "pause" is one second, and "no pause" is even less. The following syntax definition:

For other uses, see Vector Initialization.

A string can contain many Ho commands together, so that the modem can prepare for dialing or answering in the best way, such as at & amp； F & ampD2 & amp； C 1S0 = 0X4. This is called the initialization string. The V.250 specification requires all DCEs to accept a cascade command body of at least 40 characters (after "at"). The previous Hershey command set represents a great leap forward in modem-based communication. As time went on, many problems began to appear, but almost none of them were caused by the goods themselves: due to the lack of written standards, other modem manufacturers copied externally visible commands and (rough) basic commands. This leads to the nuances of how modems change their states and how they handle error conditions, hangs and timeouts. Every manufacturer tends to add new commands to deal with new requirements, which is usually incompatible with other modems.

For example, setting up a hardware or software handshake usually requires setting many different commands for different modems. This destroys the universal convenience of the basic "AT" command set. Many "Hershey compatible" modems have serious incompatibility quirks. For example, many modems need to pause for a few seconds after receiving the "AT Z" reset command. Some modems require spaces between commands, while others do not. Some will change the baud rate because of their own "will", which will make the computer not know how to deal with the incoming bits. As a result, many communication schemes finally have to give up any idea that they can talk to all "Hershey-compatible" modems, but have to try to use programs to determine the type of modems from their responses, or provide users with some methods to input any special commands to force their special modems to act correctly. The following commands are command sets supported by almost all modems, old or new. Command Description Remarks A0 or a Respond to an incoming call A/ RepeAT The last command does not use the at prefix and does not follow the carriage return. Entering a car usually means stopping. Dial the back number and shake hands.

Pulse dialing

T dial tone dialing

W— Wait for the next dial tone.

R- response mode after dialing.

@—Wait for 30 seconds and wait for the second dial.

,—Pauses in S8 register for a specified time (usually 2 seconds).

; —Maintain command mode after dialing.

! -Flash switch to hang up (hang up for half a second, and then transfer the call. )

L— Dial the last number E0 or E, and the command will not be echoed to the computer if it is not echoed. E1echo command computer (so that one person can see another person's input). H0 Hook State Hook hangs up and ends the call. H 1 On-hook state The on-hook end picks up the telephone line (usually you will hear a dial tone). I0 toI9 Investigate, notify or inquire This command returns information about the model, such as its firmware or brand name. Each number (0? 9, sometimes 10 or above) returns the modem information of a specific line, and returns "Error" if it is not defined. Today, Windows uses Plug and Play to detect the type of dedicated modem. L0 orLn (n= 1 to 3) speaker volume. Only supported by some modems, usually extended support. Modem speakers are few, or there is physical volume control, or the sound output is through the sound card. This command is not supported. Turn off or lower the volume M0 or turn off the M speaker. Silent M3 is also common when dialing, but many brands are different from M 1 remote carrier detection speakers (that is, until they are heard by other modems). M2 speaker is always on (data sound can be heard after connection). O return to online status. After the escape code of "++"is interrupted, it is restored to the normal connection state of the modem. Q0 or Q quiet mode is off-the result code is displayed, and the user will see the command response (such as OK). Q 1 quiet mode on-the result code is suppressed and the user will not see the response. Sn selects the current register

It should be noted that Sn and =r are actually three independent commands, which can be given in independent at commands. Select register n as the current register Sn? Select register n as the current register and query its value. Use? No matter which register you have selected recently, ask yourself. Sn=r selects register n as the current register and stores r in it. Use =? No matter which register is selected recently. V0 or V digital result code V 1 detailed English result code (for example, busy connection, no operator, etc. ) X0 or x result code is compatible with Heinz smart modem 300x1smart modem. Usually, the connection speed is increased to the basic result code (such as connect1200). X2 usually increases dial tone detection (to prevent blind dialing and sometimes ATO). X3 usually increases busy tone detection. X4 usually adds busy tone and dial tone detection Z0 or Z to reset the configuration stored by the modem. Multiple profiles use Z0, z 1, etc. This is the configuration of a modem without NVRAM. F. reset note: the command string is determined by the CR(\r) character. The default value of the register description range is S0. The number of rings before automatic answer is 0-0. The number of rings is 0-255, and the number of rings is 0-255. Decimal ASCII code 43 (+) S3 load return character 0- 127, decimal ASCII code 13 (load return) S4 line break 0- 127, decimal ASCII code 10 (line break) S5 backspace character 0-32. S6 Waiting time before blind dialing: 2–255 seconds; 2 S7 waiting for loading; after dialing:1–255 seconds; 50 S8 pause time (delay between dialing waiting: s 10 load loss and suspension:1–0.255 seconds 14( 1.4 seconds)). S 1 1 DTMF dialing lasts for 50-255 milliseconds 95 milliseconds S 12 code protection cancellation time 0-255 50th second 50( 1 second). S 18 test timer 0–255 seconds S25 DTR delay 0–255 seconds (seconds in synchronous mode and one hundredth of a second in other modes) 5 S26 RTS to CTS delay interval 0–255 hundredth of a second 1 one hundredth of a second S30 Inactive connection timer 0–255 seconds 0 (forbidden) S37 Required telecom line speed.

Command options:

0 attempted automatic connection mode.

1 Try to use a connection speed of 300 bits per second.

2 Try to use a connection speed of 300 bits per second.

Try to use a connection speed of 300 bit/s.

5 Try to use the connection speed of1200bit/s/s..

6 Try to use a connection speed of 2400 bits/second.

7 try to use V.23 75/ 1200 mode.

8 Try to use a connection speed of 9600 bits/second.

9 Try to use the connection speed of12000 bit/s/s..

10 tries to use the connection speed S38 of 14400bit/s to control the GSM mobile phone or modem through the at command specified in ETSI GSM 07.07(3GPP TS 27.007), with a delay of 0-255 seconds, and a delay of 20 seconds before forcibly disconnecting. The mandatory SMS message management function of GSM specified in ETSI GSM 07.05(3GPP TS 27.005).

Example of GSM command: command description AT+CPIN= 1234 Enter PIN code AT+CPWD=SC, old, newly deleted "old" PIN code "new" AT+CLCK=SC, 0, 1234 PIN code AT &；; V status ATI status (manufacturer, model, version, IMEI function) AT+COPS=? List available networks 0- unknown /2- current /3- forbidden, long name, short name, numerical value -ID, and "behavior" obtains signal strength at +CSQ. Reply +csq:

Most USB modem manufacturers, such as Huawei, Sierra Wireless and Option, have also defined proprietary wireless mode selection extensions (GSM/3G preferences) or similar extensions. For performance reasons, some of the latest high-speed modems provide virtual Ethernet interfaces instead of using PPP connections (PPP connections are only used between computers and modems, not through the network). This setting requires the vendor's AT command extension. Sometimes these specific extension specifications are public, while at other times, suppliers need an NDA to access them.