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From: "nidhi mittal hada" <nidhimittal19@gmail.com>
Sent: Wednesday, September 08, 2010 10:32 AM
To: <piclist@mit.edu>; <trupti121@gmail.com>
Subject: PIC18F4550 rs232 communication to PC

> I am a newbie to microcontroller programming I am using ccsc compiler and
> written a program to communicate to PC thru RS232 interface
> It uses users232 directive.just that ..and after that i wrote putc
> functions.
> But its not sending the character i mentioned in putc but any random
> character is coming on hyperterminal ....

I would turn the interrupts off if you are not using them - if you are=20
polling in a loop then you don't need them.
Also if you are at 9600 baud, and you are using 20MHz crystal then it's=20
likely you are loading the Tx buffer too quickly and it may be writing to i=
t=20
whilst sending the last character causing an overflow error or corrupting=20
the data. Try adding a delay between receiving and sending the character if=
=20
keeping the code as it is.
It might be a good idea to check if a character has been received by pollin=
g=20
the interrupt flag (you don't need to have interrupts enabled to do this)=20
and only sending a character if one is received.
I don't know the compiler you are using, but also check the UART and=20
Hyperterminals settings match exactly, and the *baud rate error* is=20
acceptable.
You may want to consider changing over to Hi-Tech (Microchips main compiler=
=20
now) or C18 compilers (Microchips "old" compiler - support will eventually=
=20
die out as they are promoting Hi-Tech now) as they are far more popular and=
=20
both pretty good.
Something like the below code (the definition for the interrupt flag would=
=20
be easier to use, I don't know what it is for your compiler though - if you=
=20
want to use it you will have to check what it is defined as in your=20
compiler, or look in the datasheet for the PIC and change it over)
For example in C18 it is PIR1bits.RCIF for the receive flag, it may be=20
something similar for your compiler.
If it doesn't work (I haven't had much sleep so it's very possible..) then=
=20
let us know, sure someone will get go going..


void main()
{
char c;
int i =3D 0;
set_tris_c(0xBF);
//enable_interrupts(GLOBAL);
//enable_interrupts(INT_RDA);
while(TRUE)
{

    if((PIR1 & 0b00100000) !=3D 0)   // check bit 5 (RCIF) of PIR1 to see i=
f=20
anything received
    {
        PIR1 &=3D 0b11011111;    // clear flag (cleared by reading register=
 I=20
think anyway)
        c=3Dgetc(); //if getc() timeouts 0 is returned to c
        // try a short delay like the following lines (make longer if not=20
checking flag)
        i =3D 100;
        while(i > 0) i--;
        putc(c);
    }
}
}
=20


--=20
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