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RS485.C - Send Message Question

 
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devilfrmheaven



Joined: 09 Feb 2016
Posts: 53

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RS485.C - Send Message Question
PostPosted: Sat Jun 04, 2016 11:49 pm     Reply with quote
Hi All,

First of all I am sorry I got to ask such a silly question. But can anybody help me understand the following code? I have extracted it from the RS485.c driver file.

I am not so strong in C hence I am not sure if I drew the right picture in my mind about this code.

I would like to implement the same code for my PC which would be sending the messages as Master.

Code:


int1 rs485_send_message(int8 to, int8 len, int8* data) {
   int8 try, i, cs;
   int1 ret = FALSE;

   RCV_OFF();
   #if RS485_USE_EXT_INT
      disable_interrupts(GLOBAL);
   #endif

   for(try=0; try<5; ++try) { //tries to send the message, retries 5 times if collision detected.
      rs485_collision = 0;
      fputc((int16)0x100|rs485_id, RS485_CD);
      fputc((int16)0x100|to, RS485_CD);
      fputc(len, RS485_CD);

      for(i=0, cs=rs485_id^to^len; i<len; ++i) {   //please help me understand the logic please
         cs ^= *data; //Please help me understand the logic please.
         fputc(*data, RS485_CD);
         ++data;
      }

      fputc(cs, RS485_CD);
      if(!rs485_collision) {
         ret = TRUE;
         break;
      }
      delay_ms(RS485_ID);
   }


Thanks in Advance.
_________________
Regards,
Devil
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sun Jun 05, 2016 7:19 am     Reply with quote
This post explains some of that code.
http://www.ccsinfo.com/forum/viewtopic.php?t=36810&start=3
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