You mean that modem's Tx pin goes to AVR's Tx pin and Rx goes to Rx? Then you are right, it should not be like this. You must use a cross cable that sends pin 2 signal of one side to other's side pin 3 signal and vice versa. There is no way to communicate like you described. Have you tested with the multimeter the connection between modem and PC when you connect it with the PC? Are you using the same cable in both situations?drtvskuthsav said:
No alexxx not the same cable. To connect PC and Modem am using 'Female pin to male pin connector' and am using the 'Female pin to male pin connector' if I want to check how my Controller Board when used with pc. My controller board and Modem board both are having Femal Pin DB9. So I bought a Male Pin Male Pin connector. So now I should check for the cross connection between them. I'll try it today and let you know if it worked.
In times when everything seems to fail, someone must use tools for debugging purpose. Osciloscope for hardware, debugger for software. Double check the board's configuration (like jumpers or dip switches). Then start with the osciloscope first. Go to the ATmega Tx pin. Are the serial bytes leaving this pin? Then measure modem's Rx pin. Are those bytes reaching this pin? Then modem's Tx pin and MCU's Rx pin. Follow the signal's path. In this way you will realize where the problem lies. Then you will know where to search in the program as well. If a debugger is available, it will make your life much easier. As I said the UART code seems to be OK. Maybe I missed something who knows? (even though docklight says that bytes are transmitted correctly). It happens sometimes to have a software issue, but without oscilloscope you will not know where to search for bugs in the code. You could do some measurements, share the results and then we can focus on the core of the problem, until now we are blindly searching to all of the code.drtvskuthsav said:
There must be other members following this thread as well, if someone can help I'm sure he will. I cannot ask from other members to contribute to this or any other thread. They have the free will to do so if they want to.drtvskuthsav said:
, they replaced with SIM900A which worked without any problem.
I don't think that this would be the solution, because drtvskuthsav has a problem that the modem responds to the PC, but does not respond to the exact same frames when communicating with the MCU.mpathma said:
Yes I missed this. I'll check it. I checked the SIM900 Module schematic and found that they used CTS and RTS. I'll attach the file/usermanual of SIM900 module. Please check and let me know What Changes I should do.
I fixed the baudrate at 9600 using AT+IPR and AT&W commands when connected with Hyper terminal on PC.
I don't think this would be the problem. Because MCU is printing the AT Commands as desired when connected with PC (Hyper Terminal). I've attached the Screen Shots of Commands both as Characters and Hex in my previous posts.
//*SIMTV1 Trail code for ATmega32 with SIM900 Module*//
//* KUTHSAV*//
/*VIT University, Vellore*/
/*Compiler: CodeVisionAVR*/
//*Includeing Header Files Required*//
#include <mega32.h>
#include <stdio.h>
#include <stdlib.h>
#include <delay.h>
//*Declaring LCD PORT as PORT B*//
#asm
.equ __LCD_PORT=0x18; PORTB
#endasm
#include <lcd.h>
#define baud 0x33; /* Baudrate=9600 at 8Mhz IRC Oscillator*/
#define UCB 0xD8; /*Enabling TXIE, RXIE TX and RX*/
#define LF 0x0A; /* Line feed */
#define CR 0x0D; /* Carriage Return*/
#define SUB 0x1A; /* CTRl+Z*/
/*Declaring Global Variables*/
unsigned char si=0,qi=0,i=0;
char q[160];
char ch;
void usart_init(void);
void gsmcmd(char *s);
void sendmsg(char *s);
void usart_init(void)
{
UCSRA=0x00;
UCSRB=UCB;
UBRRH=0x00;
UBRRL=baud;
}
interrupt [USART_TXC] void usart_transmit_isr(void)
{if(qi!=si)
UDR=q[si++];
}
void gsmcmd(char *s)
{
qi=0;
si=1;
while(*s)
{q[qi++]=*s++;
}
q[qi++]=CR; /*Appending Lines with Carriage Returns*/
UDR=q[0];
}
void sendmsg(char *s)
{
qi=0;
si=1;
while(*s)
{q[qi++]=*s++;
}
q[qi++]=SUB;
UDR=q[0];
}
interrupt [USART_RXC] void rx_isr(void)
{
ch=UDR;
if((ch!=0x0A)&&(ch!=0x0D))
{
lcd_gotoxy(i,0);
lcd_putchar(ch);
i++;
}
if(i>3)
{i=0;
}
}
void main(void)
{
lcd_init(16); /*lcd initialization*/
delay_ms(100);
#asm("sei") /*set enable interrupts*/
usart_init(); /*initializing USART*/
gsmcmd("AT");
delay_ms(5000);
gsmcmd("AT+CMGF=1");
delay_ms(5000);
gsmcmd("AT+CSMP=17,167,0,241");
delay_ms(5000);
gsmcmd("AT+CMGS=\"95668xxxxx\""); //*Mobile number*//
delay_ms(4000);
sendmsg("Jai Gurudev"); //*message that you want to send*//
delay_ms(2000);
}