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I should set a TC35i modem in auto answer mode to use it as a remote “serial line” for connection with a Power bar device. In practice I have to make a call to the modem and once the connection has been established I want to convey the serial line exactly as if it were connected to the PC from which the call is made.
What are the operations to be performed?
The advice is to connect the modem to the serial port of a PC using a modem cable (CBL058 * 000), on the PC run a terminal emulation program for example Toolly. Setting communication mode 9600, n, 8 send the command at to the modem and verify that it responds ok. At this point it is necessary to send: Command AT S0 = 3, to set the answer on the third ring. Command AT & D0, to force the modem to ignore the DTR signal status. Command AT & W0, to store the settings in the modem profile. Using another modem and another terminal program, make the call to the modem (Command AT DT nnnnn), and check if the string is received on the serial port RING. At the third ring the modem answers the call and begins negotiating with the calling modem. If the connection is possible the string will be returned CONNECT on both modems. From this moment all the characters sent to the serial port of the calling modem will be present in the output of the called modem and vice versa. Basically a virtual serial connection was created. To end the call, send + + + to the calling modem, this command will return it in command mode, now you can send the command AT H the call ends.
An important consideration must be made on the SIM cards to be used to make data calls with GSM modems. In order for two modems to establish a data connection, specific SIMs for M2M (Machine to machine) data connections must be used. Normal telephone SIM cards cannot be used.
If I want to use a normal voice SIM in the GSM modem, I have to make the call to the modem using a modem on a PSTN telephone line (the normal analog line), only in this case the modem will answer the call. If the call is made from an ISDN digital line or from another GSM modem, the call will not be possible.
Another consideration must be made on communication delay times. The GSM data transmission is done in packets, the data received from the serial are grouped in a packet and then sent. This type of transmission involves delays between the sending of one packet and the next. It is therefore advisable to try to have the largest possible data packages.
In practice I have seen that the communication speed is much higher between an analog and a GSM modem than that obtainable between two GSM modems.
I am trying to set auto answer on an MC35i modem. I have made all possible attempts: (ATS0 = 1..3, AT & D0, AT & W0) and others.
In order not to run the risk of having set some parameters by mistake, I have repeatedly switched to the default setting. (AT & F0). The SIM I am using is enabled for data traffic. I think, however, everything works as from the GSM modem connected in Hiper terminal and making a call to another cell phone, I see that it is a data call.
When I call the modem from any other station, I hear the dial tone and if I am connected to the Hiper terminal I see (RING). In any case, the switching to reception does not take place. I also tried typing ATA and, in this case, the modem goes to receive but no negotiation takes place. I would like to know if there is something I'm missing or if I think the modem is broken.
You have probably run into the most banal and classic of problems, you are running the tests by calling the modem from an analogue PSTN line and your SIM is a single numbered data SIM (i.e. it has a single number to which all calls are addressed, voice , data, fax).
Calls from the PSTN analog line are automatically recognized as voice calls and the modem does not respond to voice calls.
To check the operation of the modem you must make the call from another GSM modem (Always with data SIM) and in this case you will see that the modem will work.
However, there are specific SIMs for M2M communication on the market which only have data numbering and / or 2 numbers, one for data and one for faxes. Using these SIMs you can call the data number, manage the connection even from the PSTN analog line.
Well first of all a big thank you for the speed of the answer, then I think I will try to make the call from a second GSM modem as the line I use is an ISDN. In last resort I will get an M2M SIM. Anyway thanks again. PS If you have any other suggestions, it is welcome.
A suggestion that could be useful concerns the speed of the serial line, if you want to be sure that the modem serial line has a fixed connection speed (Baud rate) you have to use the command AT + IPR.
By default the modem has set the autobaud rate AT + IPR = 0, and therefore modifies the baud rate according to the data it receives from the serial line, while in autoanswer mode its baud rate must be fixed. Use for example AT + IP = 9600 to fix 9600 baud. The command AT + IPR? returns the list of baud rates supported by the modem.
The value set with the AT + IPR command is automatically saved in the non-volatile memory the modem is therefore automatically set at power on.
Same goes for the other communication parameters, number of bits and parity. The command AT + ICF set these parameters, example AT + ICF = 1 set 8 bits no parity, AT + ICF = 2, 1 sets 8 bits even parity. The command AT + ICF? returns the list of modes supported by the modem.
The value set with the AT + ICF command is stored in the volatile memory, to transfer it to non-volatile memory, use the command AT&W.
It may happen that a modem left switched on and inactive (listening to remote calls) for a long time is disconnected from the GSM network and therefore proves inaccessible. To reconnect the modem, a reconnection AT command must be sent to the modem AT+CREG=1, or turn it off and on again. Gemalto modems have introduced in their software the possibility of automatically executing timed commands, and using these commands to automatically reconnect to the GSM network.
I was trying to connect with an analog modem and a fixed telephone line (wire) with a GSM modem equipped with a "normal" WIND SIM card (not M2M) and I succeeded using the command AT + CSNS = 4 as suggested in the FAQ of a previous post (the command was sent to the modem remotely via SMS with syntax # + CSNS = 4 #). However, the forcing induced by the command is not permanent and is lost at each reset that the GSM modem performs automatically every 24 hours ... How can I make the change induced permanent with the # + CSNS = 4 # command so that it is not necessary to re-send it after each reset? I state that I have tried to make the change permanent with the commands “AT&W” and “AT ^ SMSO” (sent via SMS with syntax # & W # and # ^ SMSO #); to the first the modem replied "ok" to the second "ERROR" ... but nothing has changed it continues to reset itself losing the forcing induced by "AT + CSNS = 4" The modem is a COSTER 668 which supports AT + commands in compliance with the ETSI standard GSM 07.05 & 07.07 and V.25ter. Anyone can give me some suggestions?
Unfortunately, the COSTER GSM 668 modem manual includes only a limited number of AT commands (about 13 including some interrogation) and, please note, these do not include the "famous" AT + CSNS = 4 which has solved, at least partially, the problem, and least of all, other commands with functions such as those of AT&W.
I suspect that COSTER is just a brand that actually resells the product of others ... and that the GSM668 could actually be a "relative", perhaps revised and improved of the Siemens MC52 (which obviously I don't know). Given that the modem in question supports AT + commands in accordance with the ETSI GSM 07.05 & 07.07 and V.25ter standard, isn't there a complete list, and perhaps commented, of these commands somewhere? ... maybe some of them work ...
Thanks anyway for the support you have given me so far.
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