The string functions strstr and strchr from the c built in library string.h is very useful when we are looking for a particular string in an array of data received from UART.

The syntax are as follows:

strstr: strstr(x,y)

where x is the array which has a string of characters.
y is the string that we are looking for.
Example: strstr(x,”OK”)
This will return a pointer of first instance of string “OK” in x, otherwise a NULL

strchr: strchr(x,y)

where x is the array which has a string of characters.
y is a character that we are looking for.
Example: strstr(x,’N’)

This will return a pointer of first instance of character ‘N’ in x, otherwise a NULL

Processor: dsPIC30F4011, Compiler: MPLAB C30,

#include<p30fxxxx.h>

#include<string.h>

_FOSC(CSW_FSCM_OFF & XT);
_FWDT(WDT_OFF);
_FBORPOR(PBOR_ON & MCLR_EN);
_FGS(CODE_PROT_OFF);

#define _XTAL_FREQ 10000000UL //Crystal=10MHz,FOSC=XTAL*PLL(1)

#define FCY (_XTAL_FREQ/4) //add your operating frequency
#define BAUD_VAL(x) (((FCY/(x))/16)-1)

unsigned char Str[72], *string_loc;

void UART1_Init(unsigned int BaudRate);
void UART1_Txmt(unsigned char data);
void UART1_Puts(const unsigned char *str);
void gets_UART1(unsigned char *string);
unsigned char UART1_Receive(void);
void DelayMs(unsigned int Ms);

int main(void)
{
DelayMs(10);
UART1_Init(9600);
DelayMs(100);
UART1_Puts("Enter A String and Hit Enter:\r\n");
while(1)
{
gets_UART1(Str);
string_loc = strstr(Str,"OK");
if(string_loc) {
UART1_Puts("String \"OK\" Found@:");
UART1_Puts(string_loc);
}
else UART1_Puts("String \"OK\" Not found");
UART1_Puts("\r\n");
}
}

void UART1_Init(unsigned int BaudRate)
{
U1BRG = BAUD_VAL(BaudRate);
U1MODE = 0x8000;
U1STA = 0x8400;
_U1TXIF=0;
UART1_Puts("\033[2J"); //Clear HyperTerminal
}

void UART1_Txmt(unsigned char data)
{
while(IFS0bits.U1TXIF==0);
U1TXREG=data;
IFS0bits.U1TXIF=0;
}

void UART1_Puts(const unsigned char *Str)
{
while(*Str)
UART1_Txmt(*Str++);
}

unsigned char UART1_Receive(void)
{
unsigned char c;
while(_U1RXIF==0);
_U1RXIF=0;
c = U1RXREG;
return c;
}

void gets_UART1(unsigned char *string) //Receive a character until carriage return or newline
{
unsigned char i=0,J=0;
do
{
*(string+i)= UART1_Receive();
J = *(string+i);
UART1_Txmt(J);
i++;
}while((J!='\n') && (J!='\r'));
i++;
*(string+i) = '\0';
UART1_Txmt('\r');
UART1_Txmt('\n');
}

void DelayMs(unsigned int Ms)
{
unsigned int delay_cnst;
while(Ms>0)
{
Ms--;
for(delay_cnst = 0;delay_cnst <276;delay_cnst++);
}
}

https://www.pantechsolutions.net/microcontroller-boards/dspic-development-board