sending sms using pic16f877a and sim 300 - sms

Question

Hi I have a problem in sending message in project, I am using pic16f877a and sim300. the main function runs repeatedly. Some characters are missed in the sent sms.
my program is like this...
void main()//main function
{
Serial_init(); // initialization of serial communication
Send_SMS();
}
void Serial_init()
{
TRISC=0XC0;
TXSTA=0x24;
SPBRG=129; // set baud rate 9600 Hz for 20MHz fosc
RCSTA=0x90;
TXIF=1;
}
void Send_SMS(void)
{
USART_puts("AT\0");
putch1(0x0D);
Delay_ms4M(200);
USART_puts("AT+CMGF=1\0"); // switch into text mode
putch1(0x0D);// ascii of Carriage Return
Delay_ms4M(200);
USART_puts("AT+CMGS=\"9741153218\"\0"); // send sms to the number
putch1(0x0D);
Delay_ms4M(200);
USART_puts("Hi this is working LOL\0"); // SMS text
putch1(0x0A); // new line
Delay_ms4M(200);
putch1(0x0D);
Delay_ms4M(100);
putch1(0x1A); // ascii of 'substitute' i.e end of file
}
void USART_puts(const unsigned char *string)
{
while(*string)
putch1(*string++);
}
void putch1(unsigned char data)
{
while(TXIF==0);
TXREG=data;
}
Please help
additional details: all other programs run properly, but if I call send_sms function, "main" runs repeatedly and several messages are sent with missed characters.

Answer 1

IMHO :
Your chip is resetting. This is the highest probable cause.
Either it is faulty or you have set Watchdog Timer to on somewhere.
For missing characters :
a) Chip resets in the midst of a data transfer.
b) Roule of thumb for usart:
Stop stuffing bytes to usart. Send each byte with a small leading delay like 10-20 microseconds.
The communication is asynchronous, which means the receiver has to synchronize at the beginning of each communication unit which is a byte. To do that receiver brutely uses resources to detect start bit, the length (in time) of it etc. So if you try to send a byte train, you will stall the receiver.
Have you tried the code with another 16F877a ? (to check chip failure)...