PIC16F877A with SIM800L - uart

Question

I am having problem with PIC16F877A uart. I am trying to send AT commands to SIM800L but it is returning error. But when I try it with CP2102 module it works fine. Can anybody tell me if something is wrong with my code?
This code with similar logic is working on LPC2148 but having problem on PIC16F877A.
// CONFIG
#pragma config FOSC = HS // Oscillator Selection bits (HS oscillator)
#pragma config WDTE = OFF // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = OFF // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = ON // Brown-out Reset Enable bit (BOR enabled)
#pragma config LVP = ON // Low-Voltage (Single-Supply) In-Circuit Serial Programming Enable bit (RB3/PGM pin has PGM function; low-voltage programming enabled)
#pragma config CPD = OFF // Data EEPROM Memory Code Protection bit (Data EEPROM code protection off)
#pragma config WRT = OFF // Flash Program Memory Write Enable bits (Write protection off; all program memory may be written to by EECON control)
#pragma config CP = OFF // Flash Program Memory Code Protection bit (Code protection off)
// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.
#include <xc.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define _XTAL_FREQ 20000000
char buff[50], a = 0;
char b, *p;
int conn=0;
int i;
#define RS RD0
#define RW RD1
#define EN RD2
void lcd_cmd(unsigned char cmd)
{
PORTD = (0xF0 & cmd);
RS = 0;
RW = 0;
EN = 1;
__delay_ms(5);
EN = 0;
PORTD = (cmd<<4);
RS = 0;
RW = 0;
EN = 1;
__delay_ms(5);
EN = 0;
}
void lcd_data(unsigned char data)
{
PORTD = (0xF0 & data);
RS = 1;
RW = 0;
EN = 1;
__delay_ms(5);
EN = 0;
PORTD = (data<<4);
RS = 1;
RW = 0;
EN = 1;
__delay_ms(5);
EN = 0;
}
void lcd_string(char *str)
{
while(*str != '\0')
{
lcd_data(*str++);
}
}
void lcd_init()
{
lcd_cmd(0x02);//return to home
lcd_cmd(0x28);///4bitmode
lcd_cmd(0x0C);///cursor off
lcd_cmd(0x06);///increment cursor
lcd_cmd(0x01);///display clear
}
void uart_init()
{
TXSTAbits.TXEN = 1; ////enable transmission
TXSTAbits.BRGH = 1; ////high speed selection bit
RCSTAbits.CREN = 1; ////continuous receive enable
SPBRG = 129; ////baud rate generation 9600 at 20MHz crystal
TRISCbits.TRISC7 = 1; ////enable receive(input) on RC7
TRISCbits.TRISC6 = 0; ////enable transmit(output) on RC6
RCSTAbits.SPEN = 1; ////enable UART
GIE = 1; ///enable UART related interrupts
PEIE = 1;
RCIE = 1;
}
void gsm_send_char(unsigned char data)
{
TXREG = data;
while(PIR1bits.TXIF ==0);
}
char gsm_receive_char()
{
while(PIR1bits.RCIF == 0);
return (RCREG);
}
void gsm_send_string(char *data)
{
while(*data != '\0')
{
gsm_send_char(*data++);
}
}
__interrupt() void uart(void)
{
if(RCIF == 1)
{
b = RCREG;
buff[a] = b;
a++;
//buff[a]='\0';
GIE = 1;
RCIE = 1;
PEIE = 1;
RCIF = 0;
}
}
void gsm_init()
{
if(conn == 0)
{
a=0;
gsm_send_string("AT\r");
__delay_ms(500);
if(strstr(buff, "OK"))
{
lcd_cmd(0x80);
lcd_string(buff);
//a=0;
memset(buff, 0, sizeof(buff));
}
else
{
lcd_cmd(0x80);
lcd_string("AT ERROR");
}
}
}
void main(void)
{
TRISD = 0x00;
lcd_init();
uart_init();
lcd_cmd(0x80);
lcd_string("GSM");
while(1)
{
gsm_init();
__delay_ms(2000);
}
return;
}
I tried with changing code little bit and checked for any errors and tried to execute command on flag condition now it does not receive anything in the buffer because it does not print anything. Can anybody tell me why?
// CONFIG
#pragma config FOSC = HS // Oscillator Selection bits (HS oscillator)
#pragma config WDTE = OFF // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = OFF // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = ON // Brown-out Reset Enable bit (BOR enabled)
#pragma config LVP = ON // Low-Voltage (Single-Supply) In-Circuit Serial Programming Enable bit (RB3/PGM pin has PGM function; low-voltage programming enabled)
#pragma config CPD = OFF // Data EEPROM Memory Code Protection bit (Data EEPROM code protection off)
#pragma config WRT = OFF // Flash Program Memory Write Enable bits (Write protection off; all program memory may be written to by EECON control)
#pragma config CP = OFF // Flash Program Memory Code Protection bit (Code protection off)
// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.
#include <xc.h>
#include <pic16f877a.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#define _XTAL_FREQ 20000000
#define RS RD0
#define RW RD1
#define EN RD2
//#define AT "AT\"
char buff[80], a;
int flag, b, i = 0;
void lcd_cmd(unsigned char cmd)
{
PORTD = (0xF0 & cmd);
RS = 0;
RW = 0;
EN = 1;
__delay_ms(5);
EN = 0;
PORTD = (cmd<<4 & 0xf0);
RS = 0;
RW = 0;
EN = 1;
__delay_ms(5);
EN = 0;
}
void lcd_data(unsigned char data)
{
PORTD = (0xF0 & data);
RS = 1;
RW = 0;
EN = 1;
__delay_ms(5);
EN = 0;
PORTD = (data<<4 & 0xf0);
RS = 1;
RW = 0;
EN = 1;
__delay_ms(5);
EN = 0;
}
void lcd_string(char *str)
{
while(*str != '\0')
{
lcd_data(*str++);
}
}
void lcd_init()
{
lcd_cmd(0x02);//return to home
lcd_cmd(0x28);///4bitmode
lcd_cmd(0x0C);///cursor off
lcd_cmd(0x01);///display clear
lcd_cmd(0x06);///increment cursor
}
void uart_init()
{
SPBRG = 129;
BRGH = 1;
SYNC = 0;
SPEN = 1;
TXEN = 1;
CREN = 1;
GIE = 1;
PEIE = 1;
RCIE = 1;
RCIF = 0;
//TXIE = 1;
TRISC7 = 1;
TRISC6 = 0;
}
void gsm_send_char(unsigned char data)
{
//////////PORTB = 0xff;
TXREG = data;
while(PIR1bits.TXIF == 0);
}
char gsm_receive_char()
{
while(PIR1bits.RCIF == 0);
return RCREG;
}
void gsm_send_string(char *p)
{
while(*p != '\0')
{
gsm_send_char(*p++);
}
}
__interrupt() void isr(void)
{
if(RCIF == 1)
{
a = RCREG;
buff[i] = a;
i++;
if(a == '\r')
{
flag = 1;
}
if(OERR)
{
CREN = 0;
CREN = 1;
}
if(FERR)
{
SPEN = 0;
SPEN = 1;
}
RCIF = 0;
///////PORTB = 0xff;
}
}
void main(void)
{
TRISD = 0x00;
//TRISB = 0x00;
lcd_init();
uart_init();
lcd_cmd(0x80);
lcd_string("GSM TESTING");
while(1)
{
if(flag == 1)
{
i = 0;
gsm_send_string("AT\r\n");
__delay_ms(400);
if(strstr(buff, "OK"))
{
lcd_cmd(0xC0);
lcd_string(buff);
//memset(buff, 0, sizeof(buff));
}
else if(strstr(buff, "ERROR"))
{
lcd_cmd(0xC0);
lcd_string(buff);
// memset(buff, 0, sizeof(buff));
}
flag = 0;
}
}
return;
}
took reference from this link enter link description here
I connected PIC directly to the PC removing SIM800L and ran the code below. It was printing hello when I send hello using putty.
#include <xc.h>
#include <pic16f877a.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#define _XTAL_FREQ 20000000
#define RS RD0
#define RW RD1
#define EN RD2
char buff[80], a;
int flag, b, i = 0;
void lcd_cmd(unsigned char cmd)
{
PORTD = (0xF0 & cmd);
RS = 0;
RW = 0;
EN = 1;
__delay_ms(5);
EN = 0;
PORTD = (cmd<<4 & 0xf0);
RS = 0;
RW = 0;
EN = 1;
__delay_ms(5);
EN = 0;
}
void lcd_data(unsigned char data)
{
PORTD = (0xF0 & data);
RS = 1;
RW = 0;
EN = 1;
__delay_ms(5);
EN = 0;
PORTD = (data<<4 & 0xf0);
RS = 1;
RW = 0;
EN = 1;
__delay_ms(5);
EN = 0;
}
void lcd_string(char *str)
{
while(*str != '\0')
{
lcd_data(*str++);
}
}
void lcd_init()
{
lcd_cmd(0x02);//return to home
lcd_cmd(0x28);///4bitmode
lcd_cmd(0x0C);///cursor off
lcd_cmd(0x01);///display clear
lcd_cmd(0x06);///increment cursor
}
void uart_init()
{
SPBRG = 129;
BRGH = 1;
SYNC = 0;
SPEN = 1;
TXEN = 1;
CREN = 1;
GIE = 1;
PEIE = 1;
RCIE = 1;
RCIF = 0;
//TXIE = 1;
TRISC7 = 1;
TRISC6 = 0;
}
void gsm_send_char(char data)
{
TXREG = data;
while(TXIF == 0);
}
char gsm_receive_char()
{
while(PIR1bits.RCIF == 0);
return RCREG;
}
void gsm_send_string(char *p)
{
while(*p != '\0')
{
gsm_send_char(*p++);
}
}
__interrupt() void isr(void)
{
if(RCIF == 1)
{
a = RCREG;
buff[i] = a;
i++;
RCIF = 0;
}
}
void main(void)
{
TRISD = 0x00;
lcd_init();
uart_init();
lcd_cmd(0x80);
lcd_string("GSM TESTING");
while(1)
{
gsm_send_string("AT");
__delay_ms(400);
//i = 0;
if(strstr(buff, "hello"))
{
lcd_cmd(0xC0);
lcd_string(buff);
}
}
return;
}

Answer 1

You need to add the terminating character to the string you receive from the UART before using the strstr() function.
Something like this should work:
a=0;
gsm_send_string("AT\r");
__delay_ms(500);
buff[sizeof(buff)-1] = '\0'; // Terminate UART buffer with NULL char
if(strstr(buff, "OK"))
{
lcd_cmd(0x80);
lcd_string(buff);
//a=0;
memset(buff, 0, sizeof(buff));
}
else
{
lcd_cmd(0x80);
lcd_string("AT ERROR");
}
Depending on the compiler you are using you might also need to change the way you check for a pattern within a string. In my opinion, it would be better to do:
if(strstr(buff,"OK") != NULL)