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Serial communication for AT commands...
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Lykos1986



Joined: 26 Nov 2005
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Serial communication for AT commands...
PostPosted: Tue Feb 12, 2008 6:57 pm     Reply with quote
Hello to everyone!

I am trying to set up a communication between a Telit GM862 GSM Module and a PIC 16F877. I need a serial communication 9600 8 N 1 without hardware control (like the hyper terminal). So I am typing:

#use rs232(baud=9600, xmit=PIN_C7,rcv=PIN_C6, PARITY=N, BITS=8)

Is that right?
PCM programmer



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PostPosted: Tue Feb 12, 2008 9:42 pm     Reply with quote
Look at the pin definitions in the Overview section of the 16F877 data
sheet. (page 11 in the Acrobat reader).
http://ww1.microchip.com/downloads/en/DeviceDoc/30292c.pdf
What pin is assigned to the UART Tx and what pin is for Rx ?
Then look closely at your #use rs232() statement.
Guest
PostPosted: Wed Feb 13, 2008 3:09 am     Reply with quote
Yes… I know exactly what you mean! The transmit pin and receive pins they have to be opposite! But the problem is on hardware and I cannot change it that!

I think with the CCS we can use an asynchronous serial communication with any pins! Just software serial and not the hardware! How can I do that and also to be 9600 8 N 1?
KU5D



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PostPosted: Wed Feb 13, 2008 5:38 am     Reply with quote
If you're wanting a software UART,just pick the pins you wanna use and assign the thing to a stream such as:

#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7,stream=PC)

Then if you want to squirt something out the serial port:

fprintf(PC,"\r\n\This does a carriage return and linefeed...and prints this.");

This works on the 18F4520. I've never played with the 877 but I think they're similar in this respect.
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Confidence is the feeling you have right before you fully understand the situation...
Lykos1986



Joined: 26 Nov 2005
Posts: 68

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PostPosted: Wed Feb 13, 2008 8:32 am     Reply with quote
Ok… I start getting crazy with that project! I just want to take an “OK” respond from my Telit GM862 module! The problem is that I generally take an echo respond and not OK! What is happening?

I have post my code here:



Code:

#include <16F877A.h>
#fuses   XT,NOWDT,NOPUT,NOPROTECT,NOBROWNOUT,NOCPD,NOWRT,NOLVP
#use delay (clock=4000000)
#use rs232(baud=9600, xmit=PIN_C7,rcv=PIN_C6,PARITY=N, BITS=8,  stream=PC) //
#include <string.h>

#define L1   pin_c1
#define L2   pin_c2
#define F1   pin_e1
#define F2   pin_e0
#define power   pin_d7
#define module_led   pin_d6

char string1[10];
char string2[10];


void module_on()   //Turns on the GSM Module
{
output_high(power);
delay_ms(1200);
output_low(power);
}


void main()
{
input(module_led);
output_high(L2);

strcpy(string2,"OK");

while(1)
{
   if(input(F1))
   module_on();


   if (input(F2))
   {
      fprintf(PC, "AT\r\n");
      gets(string1);
      if(!strcmp(string1, string2))
      {
         output_high(L1);
      }
   }

}
}
Lykos1986



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PostPosted: Thu Feb 14, 2008 7:39 am     Reply with quote
Any help?
Foppie



Joined: 16 Sep 2005
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Location: The Netherlands

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PostPosted: Thu Feb 14, 2008 8:06 am     Reply with quote
most modems I know turn at command echo off with the ate0 command...

But I can advise you to make a more advanced respons filter. Maybe you should try a receiving buffer or something like that? Search this forum for something like that, I have seen several good examples in the past.
Guest
PostPosted: Thu Feb 14, 2008 8:54 am     Reply with quote
the problem is that the Telit GSM Module have got no echo by defult. So... maybe is a software error...
SET



Joined: 15 Nov 2005
Posts: 161
Location: Glasgow, UK

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PostPosted: Thu Feb 14, 2008 9:33 am     Reply with quote
I'm doing a Telit app right now, and my GM862 does echo by default..
The other poster is correct, you have to be a bit more sophisticated, get the response from the module and then parse it.
Guest
PostPosted: Fri Feb 15, 2008 7:57 am     Reply with quote
SET wrote:
I'm doing a Telit app right now, and my GM862 does echo by default..
The other poster is correct, you have to be a bit more sophisticated, get the response from the module and then parse it.



I don’t know how much sophisticated can be the code!

I was thinking that the module after the AT command will answer me just with the OK and nothing more! I was working before using only the module (not the same) and my PCs hyper terminal. The result was as I expecting! I was sending the AT command and the module answers with OK. Of course that was happening with all the other AT commands! I was not taking something more from then module! No echo not other characters…

How I can build something like that? Something that works like the hyper terminal to my PIC?
SET



Joined: 15 Nov 2005
Posts: 161
Location: Glasgow, UK

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PostPosted: Fri Feb 15, 2008 8:21 am     Reply with quote
I think you have your Tx/Rx reversed - the Telit units are a bit confusing, 'Tx' is actually the input and is therefore connected to Tx on the PIC (C6). So you can use the hardware UART.
Guest
PostPosted: Fri Feb 15, 2008 8:34 am     Reply with quote
Yes… I know that problem but I have already built my PCB. I cannot use a software UART that communicates like the windows hyper terminal?
SET



Joined: 15 Nov 2005
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Location: Glasgow, UK

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PostPosted: Fri Feb 15, 2008 8:40 am     Reply with quote
So C7 (on the PIC) is connected to Pin 25 on the GM862?
Lykos1986



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PostPosted: Fri Feb 15, 2008 9:23 am     Reply with quote
Pin 25? No…


PIC pin C7 => GM863 pin 20
PIC pin C6 => GM862 pin 37


And the the pin 45 of the GM862 to the ground, because I don’t want to use hardware flow control.




PS:
I don’t use Python, just the regular serial communication and the AT Commands
SET



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PostPosted: Fri Feb 15, 2008 9:39 am     Reply with quote
Lykos1986 wrote:
Pin 25? No…


PIC pin C7 => GM863 pin 20
PIC pin C6 => GM862 pin 37


And the the pin 45 of the GM862 to the ground, because I don’t want to use hardware flow control.




PS:
I don’t use Python, just the regular serial communication and the AT Commands


Apologies that was GC864 pinout I quoted .. (we use both!).
So your correct, your hardware is reversed. The soft UART should work Ok though, assuming 'gets ' works. If you have in-circuit debug working, can you put a breakpoint after the gets to see what string1 contains?
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