This content is part of the Serial Programming book. It covers the programming of Hayes and Hayes-compatible telephone modems. Such types of modems are the norm in.

Send SMS using AT commands. Send SMS using AT commands. Some advanced GSM modems like Wave. Com and Multitech, support the SMS text mode.

This is done by the GSM modem. Check if your GSM phone or modem supports SMS text mode. To check if your modem supports this text mode, you can try the following command. AT+CMGF=1 < ENTER>. If the modem reponds with . It is not possible.

Unicode, data and other types of messages. So the first value should be 1 or higher. This value is encoded as follows. VP + 1) x 5 minutes. Hours + ((VP- 1. 43) x 3. VP- 1. 66) x 1 day.

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VP- 1. 92) x 1 week. The third parameter contains the PID (Protocol Identifier). This parameter is only used for advanced messaging. This parameter is used to select the characterset/messagetype. When setting this parameter to '1. The modem will respond with.

You can now type the message text and send the message using the < CTRL> -< Z> key combination. Associate Software Engineer Accenture Philippines Phone. Hello World ! The modem will respond like this: +CSCS: (.

Now is the time to send the actual message: AT+CMGS=. The modem will respond with: >. The only thing you have to program by yourself, is a simple routine which converts the Unicode string to an hexidecimal string like this.

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3. History Background. Prior to the introduction of the Bulletin Board System (BBS), modems typically operated on direct-dial telephone lines that always began and ended.

Hayes command set - Wikipedia. The Hayes command set is a specific command language originally developed by Dennis Hayes. The vast majority of dial- up modems use the Hayes command set in numerous variations.

The command set covered only those operations supported by the earliest 3. When new commands were required to control additional functionality in higher speed modems, a variety of one- off standards emerged from each of the major vendors.

These continued to share the basic command structure and syntax, but added any number of new commands using some sort of prefix character – & for Hayes and USR, and \ for Microcom, for instance. Many of these re- standardized on the Hayes extensions after the introduction of the Supra. FAXModem 1. 44. 00 and the subsequent market consolidation that followed.

History. The modems operated in either . Generally, the user placing the call would switch their modem to . When the remote modem answered, already set to . To fill this role, some modems included the ability to pick up the phone automatically when it was in answer mode, and clearing the line when the other user manually disconnected. The need for automated outbound dialling was considerably less common, and handled through a separate peripheral device, a . This was normally plugged into a separate input/output port on the computer (typically an RS- 2.

This method of operation worked satisfactorily in the 1. However, the microcomputer revolution of the 1. There were potentially thousands of users who might want to dial any of the other thousands of users, and the only solution at the time was to make the user dial manually. The computer industry needed a way to tell the modem what number to dial through software.

The earlier separate dialers had this capability, but only at the cost of a separate port, which a microcomputer might not have available. Another solution would have been to use a separate set of . Both of these had hardware support in the RS- 2. However, many implementations of the RS- 2. Hayes' solution. Instead, the modem itself could switch itself between one of two modes: data mode in which the modem sends the data to the remote modem. The pause at the end of the escape sequence was required to reduce the problem caused by in- band signaling: if any other data was received within one second of the three plus signs, it was not the escape sequence and would be sent as data. To switch back they sent the online command, O.

In actual use many of the commands automatically switched to the online mode after completion, and it is rare for a user to use the online command explicitly. In order to avoid licensing Hayes's patent, some manufacturers implemented the escape sequence without the time guard interval (Time Independent Escape Sequence (TIES)). This had a major denial of service security implication in that it would lead to the modem hanging up the connection should the computer ever try to transmit the byte sequence .

For any computer connected to the Internet through such a modem, this could be easily exploited by sending it a ping of death request containing the sequence . The computer operating system would automatically try to reply the sender with the same payload, immediately disconnecting itself from the Internet, as the modem would interpret the ICMP packet's data payload as a Hayes command.

It also includes various controls to set up the modem, including a set of register commands which allowed the user to directly set the various memory locations in the original Hayes modem. The command set was copied largely verbatim, including the meaning of the registers, by almost all early 3. The expansion to 1. Hayes itself was forced to quickly introduce a 2. This re- inforced the use of the Hayes versions of these commands.

Years later, the Telecommunications Industry Association (TIA)/Electronic Industries Alliance (EIA) raised the 2. Data Transmission Systems and Equipment - Serial Asynchronous Automatic Dialing and Control, TIA/EIA- 6. However, Hayes Communications moved only slowly to higher speeds or the use of compression, and three other companies led the way here — Microcom, U. S. Robotics and Telebit. Each of these three used its own additional command- sets instead of waiting for Hayes to lead the way. By the early- 1. 99.

Things became simpler again during the widespread introduction of 1. Slowly, a set of commands based heavily on the original Hayes extended set using . Only one other command set has remained popular, the US Robotics set from their popular line of modems. Description. For example, M1. An . This extends the basic command set.

For example, & M1. Note that M1 is different from & M1. Usually starting either with a backslash (“\”) or with a percent sign (“%”); these commands vary widely among modem manufacturers. Sr=n where r is the number of the register to be changed, and n is the new value that is assigned. A register represents a specific physical location in memory. Modems have small amounts of memory on board.

The fourth set of commands serves for entering values into a particular register (memory location). The register will store a particular value (alpha- numeric information) which the modem and the communications software can utilize. For example, S7=6. In this example, .

Keep this in mind when reading the table below. When in data mode, an escape sequence can return the modem to command mode. The normal escape sequence is three plus signs (. The default value is 1. LF> Linefeed character, is the character recognised as line feed character. Its value, in decimal ASCII between 0 and 2. S4. The default value is 1.

The line feed character is output after the carriage return character if verbose result codes are used (V1 option is used); otherwise, if numeric format result codes are used (V0 option is used), it will not appear in the result codes.<..> Name enclosed in angle brackets is a syntactical element. They do not appear in the command line. Brackets themselves do not appear in the command line. When the subparameter is not given in AT commands which have a Read command, the new value equals its previous value. In AT commands which do not store the values of any of their subparameters, and so have not a Read command, which are called action type commands, the action should be done on the basis of the recommended default setting of the subparameter. Modem initialization. AT& F& D2& C1.

S0=0. X4. This is called the initialization string. Terminal- emulator software typically allows the user to send Hayes commands directly to the modem, and to see the responses.

In this example, the user of computer A makes the modem dial the phone number of modem B at phone number 5. After every command and response, there is a carriage return sent to complete the command. Modem AModem BComment. ATDT1. 55. 51. 23.

User at modem A issues a dial command: AT- Get the modem's ATtention; D- Dial; T- Touch- Tone; 1. Call this number. RINGModem A begins dialing. Modem B's phone- line rings, and the modem reports the fact. ATAComputer at modem B issues answer command. CONNECTCONNECTThe modems connect, and both modems report .

The person at computer A starts typing. The characters pass through the modem and appear on computer B's screen.

Modem B responds . The modems on both sides drop their DCD signals as well. Compatibility. This led to a wide variety of subtle differences in how modems changed from state to state, and how they handled error conditions, hangups, and timeouts. Each manufacturer tended to add new commands to handle emerging needs, often incompatible with other modems.

For example, setting up hardware or software handshaking often required many different commands for different modems. This undermined the handy universality of the basic Hayes command set. Many Hayes compatible modems had serious quirks that made them effectively incompatible. For example, many modems required a pause of several seconds after receiving the .