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parity function

 
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mshearer



Joined: 12 Jan 2009
Posts: 33

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parity function
PostPosted: Tue Jan 20, 2009 3:44 am     Reply with quote
Hi

I am using the following two functions to test the parity of a sent char.

Code:
char check_parityRCREG(void)
{

   char check_parity_result = FALSE;

    received_byte = reg_RCREG;

   if(bit_RX9D == parity_errorDetection(received_byte))
   {
      check_parity_result = TRUE;
   }
   else
   {
      check_parity_result = FALSE;
      received_byte = ZERO;
   }

   return check_parity_result;

}


Code:
char parity_errorDetection(char cms_rc_message)
{

   char rx_loop_count          = ZERO;
   char rx_bit_count           = ZERO;
   char parity_detect_result   = FALSE;

   for(rx_loop_count = ZERO; rx_loop_count < ONE_BYTE; rx_loop_count++)
   {
      if((cms_rc_message & ONE) == TRUE)
      {
         rx_bit_count++;
      }
      cms_rc_message >>= ONE;
   }

   if((rx_bit_count & ONE) == FALSE)   // Check the parity
   {
      parity_detect_result = TRUE;
   }
   else
   {
      parity_detect_result = FALSE;
   }
   return parity_detect_result;
}


the code works well for a the majority of the time. Except on the very first inputted char, also with certain combinations, such as a 'T' following a 'Y'

Considering all the variables should be zeroed at each call, i can't figure out whats going wrong.

thanks, for any help

matt
mshearer



Joined: 12 Jan 2009
Posts: 33

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PostPosted: Tue Jan 20, 2009 4:03 am     Reply with quote
and the some more needed to compile/test etc

Code:
#include <18f4520.h>
#fuses   H4,NOWDT,WDT128,NOPROTECT,NOBROWNOUT,NOPUT,STVREN,DEBUG,NOLVP,WRT,NOWRTB,NOWRTC,NOCPD,NOCPB,NOEBTR,NOEBTRB   
#use    delay(clock=40000000)
#use   rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, parity=O)
#define  ZERO       0x00
#define ONE         0x01
#define TWO         0x02
#define ONE_BYTE   0x08
#byte reg_RCREG         =   0xFAE
#byte reg_RCSTA         =   0xFAB
#bit bit_RX9D         =   reg_RCSTA.0
#byte reg_PIR1           =    0xF9E
#bit bit_RCIF         =   reg_PIR1.5
char received_byte= 0;

char check_parityRCREG(void);
char parity_errorDetection(char cms_rc_message);

void main(void)
{
   while(1)
      {
         if(bit_RCIF == TRUE)
            check_parityRCREG();
      }
}
mshearer



Joined: 12 Jan 2009
Posts: 33

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PostPosted: Tue Jan 20, 2009 5:32 am     Reply with quote
turns out my terminal program isn't sending a reliable 'odd' parity

the first 'Y' will give parity bit '0'
from then on it will give '1'

bit of a pain
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