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RS485 half duplex communication
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neverlog

Joined: 02 May 2010
Posts: 36


Posted: Sun Aug 01, 2010 5:55 pm

anyone? Please...................

PCM programmer

Joined: 06 Sep 2003
Posts: 21708


Posted: Sun Aug 01, 2010 8:16 pm

Use Google to find this information. Example: http://www.control.com/thread/1274413114 Read articles about RS-485 and Modbus: http://www.bb-elec.com/technical_library.asp http://en.wikipedia.org/wiki/EIA-485 http://en.wikipedia.org/wiki/Modbus

Wayne_

Joined: 10 Oct 2007
Posts: 681

Posted: Mon Aug 02, 2010 5:22 am

Reply with quote

First problem I see:-

Code:

char PCgetc()
{
in_char = 0;
while(!in_char);
return in_char;
}

With the above code you could miss an incomming char. If you enter this routine after a char has been recieved you will miss it:-
Try

Code:

char PCgetc()
{
char c;
while(!in_char);
c = in_char;
in_char = 0;
return c;
}

Second problem:-

Code:

int8 PCgetInt()
{
int8 i, s[3];
for(i=0; (s[i]=PCgetc()) != '\r' && i<3; ++i);
fprintf(PC,"%s",s);
return atoi(s);
}

You are trying to use s as a string but you only allocate enough storage for 3 chars, you don't initialise the array to all '\0' and your loop allows 3 chars to be read and will also terminate on a '\r' so unless the third char is a '\0' the string will not be null terminated.
You will most likely see garbage or a corruption of your data when output.
atoi will also fail.

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