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refa
Joined: 12 Dec 2003
Posts: 15
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| Having problems receiveing strings over RS232 |
 Posted: Sun Jan 11, 2004 6:03 am |
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HI group,
what I want to do is to receive a string of known characters over the RS232, 9600 bauds.
Here is my code, I made it so when I receive it I send it back to my PC to confirm the received.
| Code: |
#include <16f84a.h>
#include <stdlib.h>
#fuses XT, NOWDT, NOPROTECT
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_B1, rcv=PIN_B0, PARITY=N, BITS=8, invert)
#include <input.c>
void main()
{
char stringonja[5];
while(PIN_B0 == 0){
}
while(PIN_B0 == 1){
}
printf("test");
while(TRUE){
get_string(stringonja, 5);
printf(stringonja);
}
}
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The while(PIN_B0 == 0) and while(PIN_B0 == 1){ are made for synchronization and the sender does it too(send the 1 and 0) and I get the string "test" on my PC.
So the problem is in the get_string command because I send the string with another pic printf ("there") and on the PC I don't get anything(just "test")??
When I send the string "there" manualy like printf("t"), printf("h"), printf("e"), printf("r"), printf("e") I receive the string and see it on PC("testhere"). This way it works.
Where is my problem? May it be because I use a PIC on 4 MHz? I hope you can help me, please.
Thank you very much |
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Ttelmah
Guest
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| Re: Having problems receiveing strings over RS232 |
| Posted: Sun Jan 11, 2004 7:08 am |
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| refa wrote: | HI group,
what I want to do is to receive a string of known characters over the RS232, 9600 bauds.
Here is my code, I made it so when I receive it I send it back to my PC to confirm the received.
| Code: |
#include <16f84a.h>
#include <stdlib.h>
#fuses XT, NOWDT, NOPROTECT
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_B1, rcv=PIN_B0, PARITY=N, BITS=8, invert)
#include <input.c>
void main()
{
char stringonja[5];
while(PIN_B0 == 0){
}
while(PIN_B0 == 1){
}
printf("test");
while(TRUE){
get_string(stringonja, 5);
printf(stringonja);
}
}
|
The while(PIN_B0 == 0) and while(PIN_B0 == 1){ are made for synchronization and the sender does it too(send the 1 and 0) and I get the string "test" on my PC.
So the problem is in the get_string command because I send the string with another pic printf ("there") and on the PC I don't get anything(just "test")??
When I send the string "there" manualy like printf("t"), printf("h"), printf("e"), printf("r"), printf("e") I receive the string and see it on PC("testhere"). This way it works.
Where is my problem? May it be because I use a PIC on 4 MHz? I hope you can help me, please.
Thank you very much |
Before looking anywhere else, learn how strings are stored in C!...
A string, allways requires _one more character_ of storage, than it's length, to hold the 'null' 'end of string' character.
You are asking the program to receive a five character string, which will require six storage locations, but are only assigning five storage locations for this.
Best Wishes |
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refa
Joined: 12 Dec 2003
Posts: 15
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| Posted: Sun Jan 11, 2004 7:18 am |
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Ttelemah, thank you. I got it but wasnt the point of my problem :(!
Thank you anyways  |
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refa
Joined: 12 Dec 2003
Posts: 15
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| Posted: Sun Jan 11, 2004 11:21 am |
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Here is the new code for receiver | Code: |
#include <16f84a.h>
#include <stdlib.h>
#fuses HS, NOWDT, NOPROTECT
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_B1, rcv=PIN_B0, PARITY=N, BITS=8, invert)
#include <input.c>
void main()
{
char stringonja[10];
int a;
while(PIN_B0 == 0){
}
while(PIN_B0 == 1){
}
get_string(stringonja,10);
for (a=0; a<10; a++){
printf(stringonja[a]);
}
}
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here is for the transmitter | Code: |
#include <16f84a.h>
#include <stdlib.h>
#fuses XT, NOWDT, NOPROTECT
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_A1, rcv=PIN_A0, PARITY=N, BITS=8, invert)
void main()
{
DELAY_MS(3000); //optional :)
output_high(PIN_A1);
delay_ms(5);
output_low(PIN_A1);
printf("R");
delay_ms(2);
printf("r");
delay_ms(2);
printf("o");
delay_ms(2);
printf("k");
delay_ms(2);
printf("s");
delay_ms(2);
printf("i");
delay_ms(2);
printf("t");
delay_ms(2);
printf("z");
delay_ms(2);
printf("l");
delay_ms(2);
}
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Now I get the 9 bytes but the first one is always wrong, everytime different? Can somebody tell my why, please? Thank you  |
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refa
Joined: 12 Dec 2003
Posts: 15
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| Posted: Sun Jan 11, 2004 12:13 pm |
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I get an S insteed of R all the time(for the first byte)!! Hmm, any idea friends?
Thank you |
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Ttelmah
Guest
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| Posted: Sun Jan 11, 2004 3:46 pm |
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| refa wrote: | I get an S insteed of R all the time(for the first byte)!! Hmm, any idea friends?
Thank you |
You are still calling the 'get_string' function, with the same number of bytes defined as the size of the string.
The _max_ number in get_string, must be no more than one below the number of characters in the storage space you define. Again this is standard C.
Also the get_string function, will return when the 'max' limit is reached, or with a 'newline' character, but if this is received, this is stored.
You do not need all the 'delay_ms' calls in the transmitter, _but_ you do need the one at the end (or a slightly longer one, or a 'run off the end' trap). The 'main' function, does not loop on it's own, but will run off the end of the code. At this point, the compiler puts a 'sleep' function, hence if you send (say):
main {
printf("Test string");
}
The last two characters of the string will be lost when the chip goes to sleep. This can result in garbage characters.
Coding as:
main {
printf("Test string");
while (true) ;
}
Prevents this happening.
Now you are sending nine characters, and have the receiver waiting for ten.
What is needed, is:
[code]
TRANSMITTER
#include <16f84a.h>
#include <stdlib.h>
#fuses XT, NOWDT, NOPROTECT
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_A1, rcv=PIN_A0, PARITY=N, BITS=8, invert)
void main()
{
while (true) {
output_high(PIN_A1);
delay_ms(5);
output_low(PIN_A1);
printf("Rroksitzl/n");
delay_ms(3000);
}
}
This will send the string every three seconds.
RECEIVER
#include <16f84a.h>
#include <stdlib.h>
#fuses HS, NOWDT, NOPROTECT
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_B1, rcv=PIN_B0, PARITY=N, BITS=8, invert)
#include <input.c>
void main()
{
char stringonja[11];
int a;
while (TRUE) {
while(PIN_B0 == 0) ;
while(PIN_B0 == 1);
get_string(stringonja,10);
printf("%s",stringonja);
}
}
Best Wishes |
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refa
Joined: 12 Dec 2003
Posts: 15
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| Posted: Mon Jan 12, 2004 12:38 pm |
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| Thank you, I know that it won't loop wihtout the while(true); but I didn't know the fact about losing the last two chars when the code ends. Thank you a lot Ttelmah |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon Jan 12, 2004 1:05 pm |
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| Quote: | | I didn't know the fact about losing the last two chars when the code ends |
It turns out that CCS is not the only compiler company that has
a "secret" instruction at the end of main(), that can cause trouble.
While researching 8051 compilers, I found that Raisonance puts
a RET instruction there, which can cause more problems than the
CCS Sleep instruction. So this would be something to watch out
for, on any embedded compiler.
http://www.raisonance.com/support/faq/General/RC51_8.html |
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refa
Joined: 12 Dec 2003
Posts: 15
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| Posted: Mon Jan 12, 2004 1:25 pm |
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| Sorry but I am a beginner |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon Jan 12, 2004 1:34 pm |
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I didn't mean that as a comment about your skill level, but
more as a general comment to everyone, and myself included. |
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refa
Joined: 12 Dec 2003
Posts: 15
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| Posted: Mon Jan 12, 2004 1:39 pm |
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| Don't worry I don't take anything personal |
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refa
Joined: 12 Dec 2003
Posts: 15
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| Posted: Mon Jan 12, 2004 3:05 pm |
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Hey Ttelmah, PCM programmer and other who tried to help I still didn't solve my problem with the S insteed of R I don't know why but it might be because I transmitt the data wireless and get always another same character for another character, for number 2 I get 3, for R I get S and so on.... I can send anything as the first byte and disclude tha character in my software but I was interested why it is like that. I assume it is because of the wireless module.... 
Thank you friends for your help |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon Jan 12, 2004 3:28 pm |
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Give the manufacturer and model of the wireless module.
If possible, provide a link to their website. |
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refa
Joined: 12 Dec 2003
Posts: 15
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon Jan 12, 2004 3:55 pm |
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The data sheet has a clue.
http://www.stecom.com/files/26_BK17_1.pdf
It says there must be a pre-amble of some specified bits,
and there must be no gaps between bytes.
Also, they say you must send an XON, an XOFF, and a checksum.
I don't see that your code is doing any of this. That's probably
the reason for your problems.
The website does not appear to have any application notes.
I suggest you email them and ask for an appnote, with C source
code, which shows how to use the transceiver with a typical
micro-controller. |
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