RS232 communication PIC18f4550 -- putc sending corrupt data

[nidhimittalhada]

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.If you say i can post code also .
But its not sending the character i mentioned in putc but any random character is coming on hyperterminal ....

please help

Things i have already tried
1)enable interrupts global and INT_RDA
2)FUSES -- not sure just copied from somewhere
3)disassembled program ...disassembled program seems okay except one thing that
disassembled program dint seem to check for TMRT bit of TXSTA ...

Kindly help

[temtronic]

You don't say but you need to have a MAX232 or similar TTL to RS232 convertor chip between the PIC and the PC.
Either check with the CCS C manual or 'online' for more info.
Do help us debug your program it must be a small with fuse,and compiler version (3.xxx,4.yyy).
JAy

[Ttelmah]

Also, the 'classic' thing would be for the clock statement, to not match the real crystal being used, or the fuses are not right for the oscillator hardware involved. Async serial, is _time critical_, so everything to do with timing on the chip, must be right for it to work.....

Best Wishes

[nidhimittalhada]

[nidhimittalhada]

I have pic18F4550 rhydolabs kit, MPLAB 8.53, CCSC Compiler, HARDWARE UART with MAX232 on board.

[Ttelmah]

Several big problems.
1) You must _never_ enable an interrupt without an interrupt handler being present. Get rid of the lines doing this. I'm surprised it runs at all with these present.
2) The code talks about 'getc timeout', but you have not got this enabled in the USE RS232 line.
3) Get rid of BRG10K. This is only for chips that have the BRG problem.
4) _Is_ your crystal 20MHz?.
5) Don't delay after getting the character. If another two characters arrive in this time, the UART _will_ overrun. This will hang the UART with the code as written (add 'ERRORS' to the USE RS232 line - this should always be used with the hardware UART, unless _you_ are handling error conditions yourself.

Best Wishes

[Douglas Kennedy]

Ttelmah is right about the delay. RS232 is asynchronous and its often very smart to assume it is entirely incompatible with delays of any sort. That includes not only delay_ms but any time consuming thing like a printf. If you can't avoid using any delays then the solution is a circular buffer fed from an interrupt. The inbound int_rda is almost always needed but sometimes an output isr with a circular buffer is needed to avoid the output via rs232 blocking other processes.

[bkamen]

How about trying this:

[nidhimittalhada]

[Ttelmah]

Put ERRORS back.
You will get a _warning_, not an 'error' from the compiler. This is because when 'errors' is added, the compiler generates a variable 'rs232_errors', containing the error information, and since this is not used (at this point), the compiler generates a warning, that there is an unused variable. Warnings are just to tell you that there is something perhaps wrong going on. Problem is that not having 'ERRORS', is much worse than having one unused variable.
If you don't want the warning, simply do a dummy read of the variable at the start of your code. This will get rid of the compiler warning.

When you were 'debugging', did you actually have an interrupt handler present?. If so, then this would explain how things could work. I think part of your problem, is the RS232 overrun error, if data is arriving, and not being read. Without the 'ERRORS' directive, this _will_ lockup the UART.

The PIC2550, can run from any clock source, from 0MHz (though rather pointless), up to 25MHz with a crystal, and from an external clock input up to 48MHz. You need to find out what the actual crystal is on the board you have. Unfortunately, Rhydolabz, doesn't seem to have a current website with details of their stuff, so we can't tell what you may have. If 'echoing' characters round, it is possible for it to work with some characters, if the baud rate is completely wrong. Simply get a magnifying glass, and look at the crystal on the board. This is really the vital 'first step'.

Best Wishes

[nidhimittalhada]

Kit Spec Says ---- On Board 20 MHz Crystal Oscillator Microchip PIC 18F4550 with 20 MHz Crystal Oscillator (With Boot loader Software)
at
http://www.rhydolabz.com/index.php?main_page=product_info&cPath=99_101&
products_id=297

When I used ERRORS ...BUILD FAILED due to error not warning ... still I will try it again today.

[nidhimittalhada]

Hi
My program worked because I change use delay to 48 MHz from 20 MHz.
Thanks to you all.
As it was actually a clock problem as you all hinted.
My board
http://www.rhydolabz.com/index.php?main_page=product_info&cPath=99_101&products_id=297
says
On Board 20 MHz Crystal Oscillator.
Supports Up to 48 MHz Operation.

I was using 20MHz, thinking that is master clock
but changing it to 48 worked perfectly well.

[Ttelmah]

You can actually run at 48MHz, from the 20MHz crystal.
Fuses needed:

[bkamen]

[nidhimittalhada]

My board
http://www.rhydolabz.com/index.php?main_page=product_info&cPath=99_101&products_id=297
says

On Board 20 MHz Crystal Oscillator.
Supports Up to 48 MHz Operation.


#include <18F4550.h>
#use delay (clock=48000000)
#use rs232(baud=9600,xmit=PIN_C6,rcv=PIN_C7)

void main()
{
char c;
while(TRUE)
{
c=getc();
putc(c);
}
}

See This is the program working perfectly right.
Now It seems that my crystal is 20MHz but without using any fuses as you mentioned
My program is working well.

Even i was doubtful that it was written "in use delay give master clock "
then
On Board 20 MHz Crystal Oscillator.
Supports Up to 48 MHz Operation.
which one out of these will be called master clock
as i used 20Mhz but it did not work rightly
i then changed it to 48 M Hz it worked !!!!!

pl clarify ...