what way is best to read incoming rs232 data

[BOB_SANTANA]

Hi all
Thanks for all your help so far i am still learning the tricks of C
i just want some advise on how to go about reading in rs232 data
i have a 16bit variable that i need to update via rs232 example if i receive FFFF i want to update my variable to have the value FFFF
but i am having problem geting the data from the EX_SISR.C example
could someone please point out to me were i am going wrong
here is my program below

#if defined(__PCM__)
#include <16F877.h>
#ORG 0x1F00,0x1FFF {} // use boot loader for the 8k 16F877
#fuses XT,NOWDT,NOPROTECT,BROWNOUT, PUT, NOLVP
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7) // Jumpers: 8 to 11, 7 to 1


#define BUFFER_SIZE 32
BYTE buffer[BUFFER_SIZE];
BYTE next_in = 0;
BYTE next_out = 0;


#int_rda
void serial_isr()
{
int t;

buffer[next_in]=getc();
t=next_in;
next_in=(next_in+1) % BUFFER_SIZE;
if(next_in==next_out)
next_in=t; // Buffer full !!
}

#define bkbhit (next_in!=next_out)

BYTE bgetc() {
BYTE c;

while(!bkbhit) ;
c=buffer[next_out];
next_out=(next_out+1) % BUFFER_SIZE;
return(c);
}



void main() {

enable_interrupts(global);
enable_interrupts(int_rda);
int16 mydata;

printf("\r\n\Main Program Running...\r\n");

// The program will delay for 10 seconds and then display
// any data that came in during the 10 second delay

do {
delay_ms(10000);

while(bkbhit)
mydata=putc( bgetc() );


} while (TRUE);
}
_________________
BOB_Santana

[ckielstra]

When posting souce code please use the 'code' button, this will help to preserve formatting and makes for easier reading.

There are two problems in the code below

[Guest]

You can read the data in as a string and then convert string to hex[/quote]

[BOB_SANTANA]

[BOB_SANTANA]

Hi all
Could someone please help me with this program using serial interupts
i am trying to capture a string use the rs232 interupt but the problem
is that i want my main program to be running continously and the string captured only on interupt could you help

[PCM programmer]

A problem with your code is that instead of trying to understand
what each function does, you've just sort of tossed in lines of code
and routines. This will never work. For example, you've taken
the #int_rda routine from the Ex_Sisr.c example file, but you didn't
look at how that example determines if characters are available in
the buffer, and how it then gets characters from the buffer.
Then you've stuck in the get_string() function from Input.c, but
Ex_Sisr.c and get_string() are two different ways of getting characters.
They're not related. They don't work together. You can't just
toss them into a program and expect it to work.

[BOB_SANTANA]

Hi PCM

I did tried but was getting a bit lost in the program
from my understanding of the EX_SISR.C example
So let me start again an explain myself just give me a chance i want to understand this let take the EX_SISR.C again

[Douglas Kennedy]

The goal of the buffer is to allow the code you have in your main section to
get a chance to run with some independence of the rs232 hardware constraint that a char must be read before the next is received.
Now this could be done by a polling loop in main without using an interrupt.
The disadvantage is that a character can be received at any time so unless the loop executes fast more than one char might be received before your code gets to the point of accepting the earlier one. An interrupt avoids this providing fast capture of any received character and placement of the char in a circular buffer. The buffer may appear linear but the modulo arithmetic on the buffer size means that the placement pointer rolls over to the begining
like a dog chasing its tail. A read pointer is maintained and it also rolls over.
As the buffer fills the placement pointer moves up. As data is read the read pointer chases the placement pointer. As long as on average the read pointer can keep pace with the placement pointer the placement pointer will not lap the read pointer. So the buffer allows RS232 chars to stream into the buffer to be picked up by the read logic in main. The buffer acts like a shock or surge supressor. The data in the buffer can be read rapidly at a point of your choosing in your main code.
Now a slightly modified getc function is needed to retreive chars one at a time from the buffer. Get string opens up another issue. You don't want to make the main code wait till the whole string is received it almost defeats the purpose of using the interrupt in the first place. An approach is to set a flag in the interrupt routine to indicate when a complete string is in the buffer. To do that you need a char that indicates the end of a string could be Cr or LF. The interrupt routine will set a flag when this char is received. A modified kbhit will then check this flag before letting you main code retreive the string and will also reset it. You'll need a modified version of gets to do this
it will call your modified getc until it hits your CR or LF char

[BOB_SANTANA]

Douglas Kennedy

Thank you very much for taking the time to explain this for me.
you have improved my understanding of the whole program and i am in the process of making the suggested changes.
i would let you know how i get on should do it tonite when i get in

Best Regards
_________________
BOB_Santana

[Douglas Kennedy]

We are very fortunate on this board ... PCM programmer, Mark, Hans Wedemeyer and others have transferred much knowledge. All I knew when it came to PIC programming was that I needed to learn. PCM programmer's posts in particular have been invaluable to me and I will always be grateful.