Need help to receive string from modem !

[Guest]

Hi, I'm working on an SMS controller project. I want to be able to activate an output if a string from the modem is received.

For example if the modem replies "ok" I want to turn an LED on any time this is received. So far I've tried
strstr
strcmp
and gets

I'm using a PIC 16f876...
ANY IDEAS ?

[bkamen]

you also need to post your compiler version and a small example of your code..

In this case, we'd need to see the code that receives the string and then the code that compares it..

-Ben
_________________
Dazed and confused? I don't think so. Just "plain lost" will do. :D

[Guest]

Hi. This is the code I'm trying with. It's not working as I want though.

[Ttelmah]

OK.
First problem is s1.
You need to declare this _with enough space to hold the string you are going to receive_. At present, you are declaring it with no size, so when characters are received, these will overwrite the items in memory after this. Something like:

char s1[32];

Allocates 32 characters of storage to s1.

Second problem. ptr. This wants to be declared as a char _pointer_, not as a char. So:

char *ptr;

Third, get rid of the delay. Gets, _waits_ for a line feed to arrive. In your delay, characters _will_ be missed...

Not in what is shown, but make sure that your RS232 declaration, has 'ERRORS' in it.

Then you would normally want to display the 'waiting' message, before calling gets.

Best Wishes

[Guest]

Thanks a lot guys. The code works ! ........But I still have a problem

The number of characters to be recieved from the modem is 75 but I am only interested in the last 5. If I set

char s1[75]
char s3[75] my memory (RAM) is overloaded !

How can I ignore the first 60-65 characters ???

Here's my code

void main() {
char s1[12]; // I only want 10-15 here
char s2[] = "12345";
char s3[12]; // I only want 10-15 here
char s4[] = "54321";
char *ptr;
char *ptr2;

puts("AT");
delay_ms(1000);

puts("at+cpms=mt,mt,mt");
delay_ms(1000);

puts("at+csms=1");
delay_ms(1000);

resmsgind:
delay_ms(1000);
puts("at+cnmi=1,2,0,0,1");
goto on;



while(true){
on:
gets(s1); // If more than 12 characters are recieved, output pin 7 goes hi for itself.
ptr = strstr(s1, s2); // It can be turned off with "54321" but it doesn't turn back on.
// gets(s1) buffer is full ?
if(ptr) //
{
output_high(pin_B7);
puts("at+cnmi=1,2,0,0,1");
delay_ms(1000);
goto off;
}

if(ptr==NULL){
printf("Invalid Entry #1"); // s2 did not appear in s1
}
}
while(true){

off:
gets(s3);
ptr2 = strstr(s3, s4);

if(ptr2)
{
output_low(pin_B7);
goto resmsgind;
}

if(ptr2==NULL){
printf("Invalid Entry #2"); // s4 did not appear in s3
}
}
}

[Sal]

Can I use a delay like this to limit the characters read from the input stream ?

getch();
delay_ms(25);
gets(string);

Sal

[Wayne_]

No you can't use a delay but you can use a loop:-

[Sal]

@Wayne_

THANKS A LOT IT WORKS !!!

[Sal]

After some testing I now realise I have another issue. What happens if I ignore the 1st 60 characters but too many are entered after.

E.g I want to recieve 12345 after the first 60 characters. But if the string is 12345678, the program freezes or crashes.

I was trying to use fgets() instead of gets() but the program is not compiling.

In the above code I replaced "gets" with
fgets(s1,5,stdin); // I only wanted to read 5 characters...

This is the error
"Stream must be a constant in the valid range"

Any ideas ? or maybe there is another way ?

Thanks again for all your help

[Wayne_]

I have just noticed, your code is a bit of a mess in my opinion (before I get slated ), sorry for being so blunt but first of all I like a lot of other C programmers do not like the use of goto's in C. I have never found a reason to use them and they make the code very messy when it doesn't have to be. You may also run in to problems when you come to alter your code later on.

Now some programmers are quite happy to use goto's throughout their code in C and that is upto them but they still would not use them just for the sake of it as you do in your code.

In your code you are jumping into and out of while loops. Whilst this may work in your code (due to the fact that they are infinate while(true) loops) if you changed one of the whiles to have a condition then this would not be checked or initialised before entry into the loop.

If you want to exit a while loop, use the "break" instruction.

I have taken the liberty to re-write the main loop according to my programming style. Just have a look

[ckielstra]

[Sal]

@ ckielstra + Wayne_

Constructive criticism is one of the best tools to make a person improve. Thanks for helping...

@ckielstra

As mentioned in the start of the thread I'm doing an SMS project. My data stream is actually a 5 - digit number sent via an SMS message. The modem does not support text mode so what is recieved by the PIC is a long data stream in the form of a PDU message. Although I only want to send "12345" to activate an output, other data is sent in the PDU message such as service number etc. The total length of the string adds up to about 75 characters.

I know the data I'm sending appears as the last part of the PDU stream

e.g If I send "12345"

In PDU this is 0A07xxxxx8xx820xxxxxxxxxxxxxxxxxxxxx0127560690531D98C5603

Thats why I want to ignore all the characters before this string !

[ckielstra]

If you know the received text is always 5 digits long, then you could read all incoming data and store the data in a 5 byte buffer. On reception of each new byte you shift the data in the buffer 1 position. When you receive a CR character your value is in the buffer.

Instead of shifting the whole buffer you could use a cyclic buffer, this will be faster.