RS 232 PROBLEM

[butterfly]

hi;
i'm using pic 16f877a. 4 mhz cristall osilator.in my progrm, i descibe serial port:

#use delay(clock=4000000)
#use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8

my program is:

main() {

while(TRUE)
putc( getc()+1 );
}


WHEN I SEND A DDATA from my pc,i can see it on rc7 pin(recieve pin)..
why its not work.. any way that you can advice me??

[butterfly]

when i use:

printf("start");
its working but when use
putc('x');
it is not working.. why could you tell me?

[bsodmike]

#use delay(clock=4000000); //missing ';'
#use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8 ); //this is missing.

It should work eitherway tbh.

[PCM programmer]

[bsodmike]

Ooops,

Sorry about that PCM, was on my Mac so couldn't test but I understand Would be nice if CCS released a Mac version heh.

He's at least missing this,

#use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8) //this is missing.

...but it could just be a typo.

Would defining the ports as 'standard i/o' make much of a difference?

[Douglas Kennedy]

Lets hope Butterfly has taken the time to wire up a level shifter before asking this board for help. The PC and the PIC communicate at different polarities and voltage levels further the baud rates must match as well as the parity and stop bits. The next thing to take into account is the extensive buffering that is hidden on the PC side of things. The PIC hardware buffering is only 2 chars deep so on the PIC receive side it is very easy to overrun it with a PC.
That's why a circular interrupt driven buffer is very often necessary to have any chance of making things reliable. After the transmission of single well spaced characters is proven do not expect that moving to receiving multiple un-spaced chars will work unless you have a circular buffer. Keep in mind the buffer isn't magic so if the chars arrive on average faster than you can process them expect trouble without flow control.

[bsodmike]

Yea, wireup a max232 if you are receiving spurious data, also don't forget to decouple your ICs. I'm guessing that you've breadboarded your circuit, and the stray track to track capacitances can get quite nasty.

Some people like to just connect to the db9 connector directly or via a 1K resistor - in this case you'd want to add INVERT to your RS232 #use line, but as Douglas has pointed out - this method can cause problems and isn't a great idea if you are after reliability.

[PCM programmer]

The INVERT feature doesn't work with the hardware UART (pins C6
and C7 in this case). It will only work with a software UART.