Understanding a received SMS
1) Understanding a received SMS Frame
When your girl friend (or boyfriend! Hi to all girls) sends you an SMS like
“Get lost!” (W/o the quotes lol) do you really know what’s going on underneath (I mean in the protocol)
Let us see that now.
Let us see that now.
When an SMS is received on your phone, phone will immediately send the SMS on the FBUS to your microcontroller(in our case AT89S52), like in the excel sheet (SMS sent was “hello”). Let’s understand it.
(I will now discuss only the relevant bytes now)
Byte3=Type=SMS functions=0x02
Byte5=Frame length=0x31=odd=there has to be padding byte after Seq.No.
Byte9=Subtype of SMS functions=SMS recd=0x10
Byte10=SMS location? SIM/PHONE; 0x02=SIM
Byte11=Inbox location=0x07=7th position (will be required to delete SMS)
Byte15 to Byte 20=SMS service centre no.
e.g. The number is recd as BCD
|
15
|
16
|
17
|
18
|
19
|
20
|
|
19
|
89
|
29
|
99
|
09
|
34
|
91 98 92 99 90 43
Byte28=SMS length=0x05 (5 bytes ‘packed’sms.We will come to ‘packed’ after this)
Byte31 to Byte36=Senders number (recd same as SMS service centre no.)
Byte48=SMS data starts here and ends at offset given by Byte28.
(Seq.No. and check sums as earlier)