Attached is a fully working sample program for an SMS driven automat. You can use this example to build your own project based on it. The program and its subroutines are provided 'as is'. However you are free to remove some subroutines and add your own code but you have to be careful with others..

Dim I As Byte
Dim J As Byte
Dim K As Byte
Dim L As Byte
Dim M As Byte
Dim N As Word

The above work variables are used by diferent soubroutines and also available for use in your program. The subroutines save the original values of the variables to stack and restore afterwards.

String variables must be kept in the same order and size.  Any byte of any string variable can be addressed by using the variable Y with appropriate index.

Variable Niz is a string variable. It is used to store the commands to send to GSM and for receiving replies back. The subroutine to send the command is Poslji:

It sends the command, it clears the variable string and it sets variable X to 2, in order to prepare the index for being used in the Serial interrupt routine, which is responsible to intercept the reply.

 The Serial Interrupt routine is this:

Si_rtn:
Dim Pdubit As Bit
Dim Levi As Bit
 Bajt = Inkey()
 Scon.1 = 0
 If Bajt <> 0 Then
 If X < 10 Then : Reset Pdubit : End If
 If Pdubit = 0 Then
 If Bajt = &H0A Then : Bajt = &H2F : End If
 Y(x) = Bajt
 If Bajt <> &H0D And X < Xtext Then : Incr X : End If 'ignore carriage return
 If X > 15 And Bajt = &H2F Then : Set Pdubit : Set Levi : End If
 Else
 Bajt = Bajt - &H30
 If Bajt > 9 Then : Bajt = Bajt - 7 : End If
 If Levi = 1 Then
 Shift Bajt , Left , 4
 Y(x) = Bajt
 Reset Levi
 Else
 Y(x) = Y(x) Or Bajt
 Incr X
 Set Levi
 End If
 End If
 End If
Return

It takes some time to receive a reply from the GSM, so we should wait a bit before analizing  the reply. Instead of using wait statements, we use time interrupt driven code to do it.

We define Timer0 Interrupt procedure:

This way we get 20 interrupts per seconds using this method. So we count them at the begining of main program loop:

If we intend to send a GSM command, we use a second to send it one or two seconds after we analyze the reply:

Each 3rd second of a minute we send the command AT+CALM and we expect the reply OK in the 4th second. If the reply OK is not received, we have no connection with the GSM and we reset the bit C35i, which indicates the connection.

In a similar way we  read SMS  when it’s received:

Each 5th second we send AT+CMGL=0 Command and each 8th second we analyze the reply. If the answer is OK, then no message has arrived. If the answer is not OK, then an SMS message has been received and read into the variables Niz and Pdu ( and if message is very long also in Text). We call subroutine  Pdutxt to transform it into variables Telno and Text.

Subroutine Pdutxt to transforms information found in Niz:

+CMGL: 9,0,,23 t

into command

AT+CMGD=9

to delete the message in GSM.

In the same 8th second we call subroutine Poslji to delete the message and and we start analizing the received message, which resides in Text and of course Telno.

When we wish to send an SMS, we prepare it in Telno and in the GSM telno where the SMS is to be sent and in Text the message itself.  The actual sending is done in two phases. It has to be done in two different seconds. First we prepare the GSM handyphone for receiving a message and then we actually send the message. Therefore there are two subroutines, putsms1 and putsms2.  For actual triggering we set a bit Sendbit.

If Sekunde = 21 Then 'vsako 21. sekundo minute
 ' Če je postavljen bit Sendbit, pošljemo vsebino iz Text na Telno
 X = 2
 If Sendbit = 1 And C35i = 1 Then : Gosub Putsms1 : End If
 End If
 If Sekunde = 22 Then 'vsako 22. sekundo minute
 X = 2
 If Sendbit = 1 And C35i = 1 Then : Gosub Putsms2 : End If
 Reset Sendbit
 End If

Here’s an example of how to control some relays. There are 5 relays to be controlled

'Releji in Led diode
Rele1 Alias P1.0
Rele2 Alias P1.1
Rele3 Alias P1.2
Rele4 Alias P1.3
'Rele5 Alias P1.4
Led1 Alias P1.4
' Števci minut za releje:
Dim Relestevec(5) As Word

The appropriate counters for each relay one are minute counters. If the counter is zero, the relay is off, if not,the relay in on.

We decrement each relay-counter every minute:

If we receive a message like this:

Tr  2:30 4:6000 3:0

It should be interpreted as this command: relay2 on for 30 minutes, relay 4 on for 6000 minutes, relay 3 off immediately, the others remain unchanged,

We intercept this commant in 8th second:

If Y(xtext) = &H54 And Y(i) = &H72 Then : Gosub Tr : End If 'set rele

Subroutine Tr sets appropriate counters and afterwards prepares message about all relays counter to be sent to originator.

So after calling the subroutine, we set the bit Sendbit to trigger sending. If Command is not recognised as a valid command,  then the original SMS is sent back to originator.

Download source code here

 
I hope this will help.

Vilko Sustic