Yet another project using PIC16F877 to send & receive SM

jasonwhw · Joined: 14 Mar 2006 Posts: 8 Location: Malaysia

Hi there,

I know that there are many posting regarding this project but I could find one that can help me solve my problem. Here is my situation,

I can successfully send SMS out but I could not receive SMS. I have tested a simple program to read from serial & transmit it back using serial.

However when I connect it to my mobile phone, I can't seem to receive the SMS. I'm using 4MHz crystal with 9600 baud rate.

Btw, I am using a MAX232 as an interface between the PIC and the mobile phone (Ericsson T610).

Just so that you are interested to see my code. Here it is,

Ttelmah · Guest

First comment. You don't need 'kbhit'. If the RDA interrupt is called, it is because there _is_ data waiting.
Now comes the 'yetch' bit.
Each array access, is going to involve something like ten machine cycles. You have eight such accesses, in the first 'if', and if this fails, another similar sequence, and then yet another. With the global overhead, the interrupt handler here, is going to reach something in the order of possibly 500 or more instruction cycles, and depending on what is inside the 'send_sms1', 'send_sms2', and 'check' routines, probably vastly more. This is an almost certain fomula for failure...
On top of this, you have a problem that these accesses will address illegal values. On the first pass for example, when you look 'seven bytes back', you will access effectively a negative index into the array, which will 'wrap' (because of integer arithmetic), and will access address 249 in the array, which will probably be somw other variables...
Approach this very differently. First, handle the RS232 transmission, via an interrupt driven buffer. I have posted code to do this on several occassions in the past. This way, assuming that the 'send' routines actually transmit something on the RS232 (as the printf already does), you will not get delayed in the receive routine, waiting for the transmissions to occur.
Then in your receive code, use a state machine. A search here, will find examples of these published in the past. Alternatively, do the decode check, outside the interrupt handler, just setting a flag, when a complete packet has arrived.

Best Wishes

jasonwhw · Joined: 14 Mar 2006 Posts: 8 Location: Malaysia

So you are suggesting that I should use a buffer for transmission thru RS232. As for the receive code, use a state machine or decode incoming data outside the int_rda interrupt handler.

Do you think you could provide me with the sample code for interrupt driven buffer and the state machine? You will be so nice you could do that for me. Many thanks....

PICoHolic · Joined: 04 Jan 2005 Posts: 224

jasonwhw,

Could you plz tell me how did u get the pin configuration of your mobile device and how did u get the serial command to send & get SMS?

10x

jasonwhw · Joined: 14 Mar 2006 Posts: 8 Location: Malaysia

each mobile phone has their own pin configuration.try search the net.you should be able to find your mobile pin configuration.you can send & receive SMS by using AT command.it is a command used for modem.try search the net again for more info on that.different mobile phone might have different AT command.

jasonwhw.

PICoHolic · Joined: 04 Jan 2005 Posts: 224

Thank you

HuaWuQue · Joined: 20 Jan 2006 Posts: 5

hi jasonwhw,

im doing a project which quite similar with u, but i'm using ToothPIC microcontroller. so the connection b/w toothPIC and mobile phone is via bluetooth, no MAX232 is needed.

could u share ur source code of sending sms at here?

i had posted a thread bout my project as well. hope u can give opinion.

http://www.ccsinfo.com/forum/viewtopic.php?t=26238

thanks.