So far I’ve show how to send a text message in PDU mode. There is nothing special about this. There are a number of things you can do in PDU mode, that you can’t do in text mode.
A first example is a flash SMS message.
A flash SMS message is an SMS message that, instead of being stored in the SIM or memory of the receiving phone, pops-up on the receiving phone’s screen, without the user taking any action. When dismissed the message is usually gone.
Here is an example AT command to send a flash SMS message in PDU mode:
AT+CMGS=28<crlf> > 0001010B915121551532F40010104190991D9EA341EDF27C1E3E9743<Ctrl-Z>
Here is what the individual octets represent:
| Size | Value | Description |
| 1 octet | 00 | We don’t supply a SMSC number. |
| 1 octet | 01 | PDU type and options. This is a plain SUBMIT-PDU. |
| 1 octet | 01 | Our message reference. |
| 1 octet | 0B | Size of the destination telephone number (in digits) |
| 1 octet | 91 | International numbering plan. |
| 6 octets | 5121551532f4 | This represents the destination and it translates to 1 512 555 1234 |
| 1 octet | 00 | Protocol identifier. |
| 1 octet | 10 | Data Coding Scheme. This is the value that causes the message to be a flash message as opposed to a standard SMS. |
| 1 octet | 10 | User Data Length or payload size (in characters). |
| 16 septets | 4190991D9E A341EDF27C 1E3E9743 |
The payload, also known as User Data. In this case, it is just GSM encoded text. This particular string represents “A flash message!”” |
A more elaborate explanation of the GSM encoding and other fields is giving in a previous post in this series.
