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ntrungtruc2003
Joined: 16 Feb 2011
Posts: 42
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| can not receive the true character from pc |
 Posted: Fri Feb 18, 2011 11:27 am |
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Dear Sir
I sent an ascii character(ex 'A') from PC to PIC16F877A and store the received value to char c. Both sent value and received value are equal.
(pc:A-----rs232------pic:A).
But when i store the received value to buffer[next_in]. The reveived value not equal to sent value.
(pc:A(41H)-----rs232------pic:1)
I use a lcd(16x2) to display the received value for test.
Can you teach me how to solve it. I also try to use %c or %d or %x in printf(lcd_putc,"%c", buffer[next_in])
| Code: |
#include <16f877A.h>
#fuses HS, NOLVP, NOWDT, NOPROTECT
#use delay (clock=8000000) //Use built-in function: delay_ms() & delay_us()
#use rs232(baud=9600,parity=N, xmit=PIN_C6, rcv=PIN_C7, bits=9)
#include "LCD_TM.c" //use module function
#define BUFFER_SIZE 32
char buffer[BUFFER_SIZE];
int next_in = 1;
#int_rda
void receiver_isr(void)
{
buffer[next_in]=getch();
putc(buffer[next_in]);
next_in++;
}
void main(void)
{
lcd_init();
enable_interrupts(int_rda);
enable_interrupts(GLOBAL);
printf("hello");
while(true){
//lcd_init();
lcd_gotoxy(2,1);
printf(lcd_putc,"%x",buffer[next_in]); // here is problem.
lcd_gotoxy(1,2);
printf(lcd_putc,"");
delay_ms(20);
}
} |
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FvM
Joined: 27 Aug 2008
Posts: 2337
Location: Germany
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| Posted: Fri Feb 18, 2011 11:45 am |
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| buffer[next_in] is not the last character received. |
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ntrungtruc2003
Joined: 16 Feb 2011
Posts: 42
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| Posted: Fri Feb 18, 2011 12:14 pm |
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Thanks for your reply.
Could you explain me?. The first received value is also different.
I just send one character and terminate. |
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FvM
Joined: 27 Aug 2008
Posts: 2337
Location: Germany
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| Posted: Fri Feb 18, 2011 12:20 pm |
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| After next_in++ buffer[next_in] is an empty location. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19496
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| Posted: Fri Feb 18, 2011 3:26 pm |
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First comment. In C, arrays start at '0', not 1.
Then think about it. One character received starting from '1' as you currently have:
Character received - > buffer[1]
next_in now equals 2 - This is the _next_ location, where a character is _going_ to be put. Trying to read 'buffer[2]', just gets garbage (depends what happens to be sitting in the memory, when the chip wakes up.....).
Look at ex_sisr, for an example of how to handle a 'circular buffer' like this. _Two_ addresses are needed. 'next_in', and 'next_out'. The numbers 'chase' one another, with next_out incrementing _after a character is read_, and next_in incrementing after a character is written.
Best Wishes |
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ntrungtruc2003
Joined: 16 Feb 2011
Posts: 42
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| Posted: Sat Feb 19, 2011 4:09 am |
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It's worked. He he Thanks your very much.
here is code
| Code: | #include <16f877A.h>
#fuses HS, NOLVP, NOWDT, NOPROTECT
#use delay (clock=8000000) //Use built-in function: delay_ms() & delay_us()
#use rs232(baud=9600,parity=N, xmit=PIN_C6, rcv=PIN_C7, bits=9)
#include "LCD_TM.c" //use module function
#define BUFFER_SIZE 32
BYTE buffer[BUFFER_SIZE];
BYTE next_in = 0;
BYTE next_out = 0;
byte c;
#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(void)
{
lcd_init();
enable_interrupts(int_rda);
enable_interrupts(GLOBAL);
printf("hello");
while(true){
//lcd_init();
lcd_gotoxy(2,1);
c = bgetc();
printf(lcd_putc,"%c",c); // here
lcd_gotoxy(1,2);
printf(lcd_putc,"hello");
delay_ms(20);
}
} |
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