Data trasmissione with GSM

Thread view:

Enable EMail Alerts

Start New Thread

Thread rating:

Maverick - 21 Jan 2004 15:43 GMT

Hi,
I'm trying to send some data trought 2 gsm modems.

Every Modem is link trought a serial cable to a computer, I use
Hyperterminal to send at commands.

On the first modem I send at+cops? and I see that this modem is correctly
registered

On the second modem , I send at+cops? and I see that this modem is correctly
registered, then I use the atd... command and after the handshake I receive
the Connect 9600 on all 2 modems.

This is the question: Sometimes I start to send caracters and I see them
coming on other Pc in 2 or 3 seconds, othertimes I send characters that will
never arrive on other PC.

WHY?

I need to use other AT command to set correctly the modems?
Someone can help me providing a list of at commands used to initialize 2
modems?

Notes:
2 modem are into one office and are stopped.
I use my nokia 7110 to test the network level and the network level is at
the top!

Thanks in advance.

Reply to this Message

John Henderson - 23 Jan 2004 04:59 GMT

> Hi,
> I'm trying to send some data trought 2 gsm modems.
[quoted text clipped - 14 lines]
>
> WHY?

I have no idea. If they weren't echoing on the *sending* system,
that would likely be a matter of turning echo on.

> I need to use other AT command to set correctly the modems?
> Someone can help me providing a list of at commands used to
> initialize 2 modems?

GSM standards can be downloaded free from www.etsi.org (after
registering). GSM 07.07 specifies the general GSM cellular
extensions to the standard AT command set (GSM 07.05 has further
commands related to text messaging).

Go to the download area, search for "07.07", and download a
recent version from the unsorted list.

> Notes:
> 2 modem are into one office and are stopped.
> I use my nokia 7110 to test the network level and the network
> level is at the top!

As you're using Nokias, see also:
http://ncsp.forum.nokia.com/downloads/nokia/documents/AT-help.pdf.

John

Reply to this Message

Maverick - 23 Jan 2004 11:35 GMT

Thanks John.
This list is very useful.
I see all gms commands and all seems to be Ok.

I'm wondering if someone can provide me with some example of list of command
to initialize.

Example:
I now use:

at+cpin?
...
at+creg=1
at+cops=0,2
at+cbst=7,0,1

is there any other command that GSM need to obtain a secure connection?
Thanks in Advance!

Reply to this Message

John Henderson - 23 Jan 2004 22:39 GMT

> I'm wondering if someone can provide me with some example of list of command
> to initialize.
[quoted text clipped - 7 lines]
> at+cops=0,2
> at+cbst=7,0,1

Many people use and recommend a standard 9600 bps fixed modem
driver with GSM phones. I use an old Siemens S25 driver, which
contains the following initialization sequence:

AT&FE0V1&D2&C1Q0S0=0

As you can see, it contains no cellular-specific commands (no
"+C" AT commands).

John

Reply to this Message

Chris - 24 Jan 2004 10:56 GMT

could it be that the modems have hardware handshaking and this is not
configured correctly?

if RTS line is in the wrong state then you may still be able to get command
mode responce to see you are on the network etc. but data will be held
waiting the correct state of RTS line.

Chris

> Hi,
> I'm trying to send some data trought 2 gsm modems.
[quoted text clipped - 25 lines]
>
> Thanks in advance.

Reply to this Message

John Henderson - 24 Jan 2004 18:09 GMT

> could it be that the modems have hardware handshaking and this
> is not configured correctly?
>
> if RTS line is in the wrong state then you may still be able to
> get command mode responce to see you are on the network etc.
> but data will be held waiting the correct state of RTS line.

Yes, I agree that some sort of flow-control problem could cause
the failure to pass characters. Without knowing the setup, a
cheap (poorly-specified) data cable could trigger such errors.

John

Reply to this Message