sending long sms messages

hello there,
I want to learn how to send an sms message more than 160 chars by AT+CMGS command in text mode.
How can I do that ? When I try to do that, modem gives me ERROR message. I can easly send smses with less than 160 chars by the way.


As far as I’m aware, SMS is limited in the GSM spec to 160 7 bit characters.

The default method of sending SMS is via TEXT mode - which limits you to the 160 characters

There is another SMS mode called PDU mode, which encodes the text of the SMS. From my reading, long SMS messages are sent by

  • encoding the text
  • breaking the encoded message into the appropriate sized chunks
  • wrapping these chunks inside a PDU message with the header indicating that there is more than one chunk to the message.

Each chunk is sent as a separate SMS (so a logical message may consist of more than one physical SMS) - and reassembled by the receiving device. Usually, each physical SMS is billed by the telco appropriately.

You’ll have to have a look in the AT commands guide for your module to confirm if it supports PDU mode.

Hope this helps.

Ciao, Dave

Thank you for your explanation. I understood that i need to send sms with PDU mode. First of all, i learnt how to send an sms with PDU mode. Then i started to search about combining SMSes.
I found this link about sending multiple smses.
I think there is UDH(user data header) in PDU string that we need to set. If someone needs the same thing, he can follow the link above.