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I used to have an SIM800l module that I do not know exactly how I set up, but every time I deleted a SMS from the first memory location, the other SMS were moved up to the position of the first SMS, always occupying the position number one in storage.

Does anyone know how to set up my new module like that?

With such setup, in order to delete all SMS, I just repeatedly sent the command AT+CMGD=1 so that I didn't need to change the indices.

Roberto Caboni
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mohammad bagher Malekhosseini
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1 Answers1

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SMS messages changing position sound really strange, and I'm not sure it was what actually happened. Read all my answer to discover what I think could be the actual explanation.

TL;DR: you are lucky, because you can free your SMS memory with a single command: AT+CMGDA.

According to AT command guide its syntax is really simple:

AT+CMGDA=<type>

where <type> has a different meaning according to the +CMGF setting.

In text mode (after AT+CMGF=1):

  • "DEL READ" - Delete all read messages
  • "DEL UNREAD" - Delete all unread messages
  • "DEL SENT" - Delete all sent SMS
  • "DEL UNSENT" - Delete all unsent SMS
  • "DEL INBOX" - Delete all received SMS
  • "DEL ALL" - Delete all SMS

In PDU mode (after AT+CMGF=0, that's not actually required, as it is the default value):

  • 1 - Delete all read messages
  • 2 - Delete all unread messages
  • 3 - Delete all sent SMS
  • 4 - Delete all unsent SMS
  • 5 - Delete all received SMS
  • 6 - Delete all SMS

What you need is to provide

AT+CMGDA="DEL ALL"

if you are operating in text mode, or

AT+CMGDA=6

if you are operating in PDU mode.

Even better, you can get rid of just read messages by issuing

AT+CMGDA="DEL READ"

if you are operating in text mode, or

AT+CMGDA=1

if you are operating in PDU mode. I suspect the latter was the command you actually used to provide.

Roberto Caboni
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