Codes to receive RS232 data from COM 1 of PC FAILED

[ernest]

I have written the following codes to check the data received by the PIC16F877A from COM 1. Basically, it echoes the data signal that it received back to the PC for us to view and verify.

However, this program does not work most of the time. On a few occasion, it echoes some irrelevant data.

Please help...


#include <16F877A.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=20000000)
#use RS232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)

#include <input.c> //found in the CCS drivers example//

#define KEYHIT_DELAY 500 // in milliseconds ie 500 ms


char timed_getc() {
long timeout;
char retval;

timeout=0;
while(!kbhit() && (++timeout< (KEYHIT_DELAY*100)))
delay_us(10);
if(kbhit())
retval = getc();
else
retval = 0;
return(retval);
}



//================================
void main()
{
int status, i;
char value;
//char valid[11] = {'1','2','3','4','5','6','7','8','9','0'}; tried this but can't work
char valid;


long int temp, hum;
long int store[3];


while(TRUE)
{
status=1;
printf("\r\nStart typing:\r\n");
while(!kbhit());

while(status==1)
{
value=timed_getc();
if(value==0)
status=0;
else
{
status=1;
putc(value);


switch (value)
{
//Tried the following but can't work
// CASE valid:
// store[i] = buffer - 0x30 (with this you will store the integer )
// i++;
// BREAK;

CASE '0':
store[i] = value - 0x30; //Value(ASCII format) - 0x30 = Value(decimal)
i++;
BREAK;

CASE '1':
store[i] = value - 0x30;
i++;
BREAK;

CASE '2':
store[i] = value - 0x30;
i++;
BREAK;

CASE '3':
store[i] = value - 0x30;
i++;
BREAK;

CASE '4':
store[i] = value - 0x30;
i++;
BREAK;


CASE '5':
store[i] = value - 0x30;
i++;
BREAK;


CASE '6':
store[i] = value - 0x30;
i++;
BREAK;

CASE '7':
store[i] = value - 0x30;
i++;
BREAK;

CASE '8':
store[i] = value - 0x30;
i++;
BREAK;


CASE '9':
store[i] = value - 0x30;
i++;
BREAK;

CASE 'C':
temp = 100*store[0] + 10*store[1] + store[2];
i = 0;
printf("%04ld Celcius",temp);
BREAK;

CASE '%':
hum = 100*store[0] + 10*store[1] + store[2];
i = 0;
printf("%04d percent",hum);
BREAK;
}
}


}
printf("\r\nToo slow!\r\n");
}
}

[Kasper]

try making it interrupt based, this way you can also make the pic do other stuff while waiting for incomming characters.

here is a code snippet, which does work for returning your characters.
It is set up to use the two hardware UARTS in the 18F6720, but on the 16F877 if you have only one, comment out the one you don't have.

As far as I am concerned, Interrupts are the way to go for RS232 communications