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sean_tpc
Joined: 21 Aug 2008
Posts: 10
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| Comparing two strings over RS232 |
 Posted: Tue Sep 23, 2008 5:40 am |
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As a newbie specially on PIC-C programming, I have difficulty on comparing two strings of characters received form pc via RS232. Here's some part of my code: | Code: | /
/*******************************************************************************
Variables
*******************************************************************************/
byte DATA_IN =0; //write data register
byte DATA_OUT =0; //read data register
byte DATA_RCV =false; //mask for DATA_IN recieve
byte BANK1 =0; //pntr for EEPROM read @ bank 1
byte BANK2 =0; //pntr for EEPROM read @ bank 2
byte SAME =FALSE; //mask for same string recieve
byte i_1 = 0xA0; //start offset of user data bank register
byte i_2 = 0; //end offset of user data bank register
byte i_3 = 0x120;
*******************************************************************************
Interrupt from RS232
*******************************************************************************/
#int_RDA
void RS232_isr(){
DATA_IN = getc(); //get character from RS232
write_bank(1,i_1, DATA_IN); //save to bank1
putc(DATA_IN); //send recieve byte
i_2 = i_1; //Increment 'till end
DATA_RCV = TRUE; //mask DATA_IN recieve
output_high(RCV_CHAR_STAT);
}
/*******************************************************************************
Process data receive over RS232
*******************************************************************************/
void CHECK_DATA_RCV(){
byte i=0;
if (DATA_RCV==TRUE){ //Do i recieve data from RS232?
delay_ms(100); //..yes
/**************************************************************
/ Check for the first string recieve /
/*************************************************************/
BANK1=0xB2;
BANK2=0x121;
if (read_bank(2,BANK2)==0){
i_1=0xA0;
i_3=0x120;
do{
DATA_OUT = read_bank(1,i_1++);
if (i_1>0xB2) //start copy at address 0xB2
write_bank(2,i_3++,DATA_OUT); //save to bank2
} while(i_1!=i_2);
}
/**************************************************************
/ Compare 2 strings , if not the same do something /
/*************************************************************/
else{
BANK1 = 0xB2; // set pntr for read EEPROM operation
BANK2 = 0x120;
i=0;
do{ // compare string recieve from previous one
i++;
if(read_bank(1,BANK1++) == read_bank(2,BANK2++))
SAME =0 ; // the same string recieve ?
else { SAME =1 ;
i =15; }
}while(i !=15 );
if (SAME ==0 ) // if the same string then do nothing!.....
{ ; }
else
{SAME =0 ; // clr flag
lcd_putc("Strings not the same");
i_1 = 0xA0 ;
i_3 = 0x120 ;
do{ // save new string to from BANK_1 to BANK_2
DATA_OUT = read_bank(1,i_1++); // read byte @ BANK_1
if ( i_1 >0xB2 ){
write_bank(2,i_3++,DATA_OUT); //Save to Bank2
}
else;
} while(i_1 !=i_2);
}
}
DATA_RCV=FALSE;
}
}
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I'm using CCS ver 4.074
MCU: PIC16F876
OCS 16Mhz |
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Wayne_
Joined: 10 Oct 2007
Posts: 681
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| Posted: Tue Sep 23, 2008 7:06 am |
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Where is the i_1 increment in your isr ?
You also use i_1 var in your CHECK_DATA_RCV() routine. If a char came in on the rs232 during this routine it would corrupt your buffer. |
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Ttelmah
Guest
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| Posted: Tue Sep 23, 2008 9:13 am |
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Another problem. You seem to be trying to write the RS232 data to EEPROM.
EEPROM writes are _slow_. Typically 4mSec, and as much as 8mSec. You don't show the baud rate, but at 9600bps, a character can arrive every 1.04mSec. This will result in lost data (and possibly UART lock up). Also the write life of EEPROM is relatively low. Writing one byte every 4mSec, will destroy the EEPROM, in typically 400 seconds....
Best Wishes |
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sean_tpc
Joined: 21 Aug 2008
Posts: 10
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| Posted: Wed Sep 24, 2008 2:21 am |
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Thanks a lot guys. Here's my working code: Any suggestion the best way to do it? Maybe a simple example will be a great help. This code below can compare string of text w/ 33 characters only | Code: | #include <16F876.h>
#device icd =true
#fuses HS,NOWDT,NOPROTECT,NOLVP
#ocs 16 Mhz
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
#include <LCD_Driver876.h>
BYTE value_1 = 0; // pntr for EEPROM read @ Bank_1
BYTE value_2 = 0; // pntr for EEPROM read @ Bank_2
BYTE data_in = 0; // data register (write)
BYTE data_out = 0; // data register (read)
BYTE byte_recieve = 0; // mask recieve_byte operation
BYTE i_1 = 0xA0; // start recieve byte pointer register
BYTE i_2 = 0; // end recieve byte pointer register
BYTE i_3 = 0x120;
BYTE SAME_TXT = false; //Flag to compare recieve string
#define SYS_LED PIN_B3 //System LED indicator
#define RCV_STAT PIN_B2 //Recieve character indicator
/*************~-MCU Status indicator-~*************************************************************/
void MCU_STAT(){
output_toggle(SYS_LED);
delay_ms(200);
}
void EXECUTE_SOMETHING(){
lcd_putc("\fNot the same\nstring recieve!");
}
void NO_EXECUTE(){
lcd_putc("\fSame string\nrecieved....");
}
/*************~-Interrupt from RS232-~*************************************************************/
#int_rda //interrupt for Rx
void serial_isr(){
data_in = getc(); //Get character from rs232
write_bank(1,i_1++,data_in); //Save to BANK_1
putc( data_in ); //Send string of characters to PC2
i_2 = i_1; //increment begin(i_1) to end (i_2) pointer
byte_recieve = 1; //mask recieve operation
}
/************~-Recieved string processing function-~***********************************************/
void CHK_STRINGS(){
int i =0;
if(byte_recieve == 1) //do we recieve byte?
{ //yes.
delay_ms(100);
/*************~-Check for first recieve characters-~***********************************************/
value_1 = 0xB2;
value_2 = 0x121; //if from power up,.. first recieve ?
if ( read_bank(2,value_2) == 0 )
{
i_1 = 0xA0 ;
i_3 = 0x120 ;
do{ // save batch to BANK_1
data_out = read_bank(1,i_1++); // read byte @ BANK_1
if ( i_1 >0xB2 ) // start copy at address 0xB2
{ write_bank(2,i_3++,data_out); } // save to BANK_2
else;
} while(i_1 !=i_2);
}
/*************~-Compare two strings.. if not the same execute something-~**************************/
else{
value_1 = 0xB2; //set pntr for read EEPROM operation
value_2 = 0x120;
i=0;
do{ //compare string recieve from previous one
i++;
if ( read_bank(1,value_1++) == read_bank(2,value_2++) )
{ SAME_TXT =false ; } //the same string recieve ?
else { SAME_TXT =true ;
i =15; }
}while(i !=15 );
if (SAME_TXT ==false) //if the same string then do nothing!.....
NO_EXECUTE();
else{
SAME_TXT =false ; //clr flag
EXECUTE_SOMETHING();
i_1 = 0xA0 ;
i_3 = 0x120 ;
do{ //save new batch to from BANK_1 to BANK_2
data_out = read_bank(1,i_1++); // read byte @ BANK_1
if ( i_1 >0xB2 )
{write_bank(2,i_3++,data_out); } // save to BANK_2
else;
}while(i_1 !=i_2);
}
}
i_1 = 0xA0;
i_2 = 0; //clr the two pointer
i_3 = 0x120;
byte_recieve = 0; //unmask recieve_byte operation
output_high(RCV_STAT); //set character recieve LED on
delay_ms(800);
output_low(RCV_STAT); //clr character recieve LED on
}
}
/*************************~-MAIN PROGRAM-~*********************************************************/
#zero_ram
void main(){
lcd_init();
enable_interrupts(global);
enable_interrupts(int_rda);
for(;;){
MCU_STAT(); //MCU status indicator
CHK_STRINGS(); //Check recieve strings from pc1
}
} |
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sean_tpc
Joined: 21 Aug 2008
Posts: 10
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| Posted: Fri Sep 26, 2008 3:13 am |
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| Any good suggestions!? Maybe a good example will help....pls |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Fri Sep 26, 2008 9:30 am |
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Some remarks on your code: | Code: | | #use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7) |
Add the ERRORS directive to this line. Doing so causes the compiler to create code for clearing the UART's error flags on every call to getc(). Without this keyword you are running the risk of the UART stopping on receive buffer overflow (only 3 characters).
This is a bug, the maximum value fitting a byte is 0xFF.
| Code: | BYTE value_1 = 0; // pntr for EEPROM read @ Bank_1
BYTE value_2 = 0; // pntr for EEPROM read @ Bank_2 |
Call the things by their right names. These are pointers to RAM banks, not to EEPROM.
| Code: | if(byte_recieve == 1) //do we recieve byte?
{ //yes.
delay_ms(100); |
Why is the delay of 100ms here? It is wasting processor time. Besides that, in the mean time more data is received and you might even get a receive buffer overflow, resulting in data loss.
The use of the functions read_bank and write_bank is only recommended for situations with special memory requirements. Problem of using these functions is that they are very low level and the compiler can not warn you for errors.
Your PIC16F876 can easily handle RAM buffers up to 80 characters so there is no need to use these low level functions. Simply allocate RAM by using an array:This reserves memory for 30 bytes.
Enable the compiler to use 16 bit pointers. This will allow for larger RAM buffers.
Another improvement to your program would be to have the received string start and stop with a known character. This makes it a lot easier to synchronize the sender and receiver. For example, have the sender start the string with ASCII value STX (Start of Text, 0x02) and end the string with a linefeed character (LF, 0x0A).
Here is a test program that will display a text every time a new message is received. The message should start with a 0x02 and end with a linefeed (0x0A) character. The program compiles but is not tested.
| Code: | #include <16F876.h>
#device icd =true
#device *=16
#fuses HS, NOWDT, NOLVP, NOPROTECT
#ocs 16 Mhz
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
#include <string.h>
enum RECEIVE_STATES {IDLE, RECEIVING};
enum RECEIVE_STATES receive_state = IDLE;
#define STX 0x02
#define LINEFEED 0x0A
#define MAX_STR_LEN 40
char RxBuff[MAX_STR_LEN + 1]; // +1 for terminating zero.
int8 rxBuffPtr = 0;
int8 new_string_received = FALSE;
char StringBuffer[MAX_STR_LEN + 1]; // +1 for terminating zero.
// Compare the new received string to the previous string.
// If a new string is found than the string is copied for comparison next time.
void CheckForNewString()
{
if (strcmp(RxBuff, StringBuffer) != 0)
{
// New string found, copy the string and set flag.
strcpy(StringBuffer, RxBuff);
new_string_received = TRUE;
}
}
// Interrupt from RS232 receiver
#int_rda
void serial_isr()
{
char data_in;
data_in = getc(); // Get character from rs232
putc( data_in ); // Echo character to PC2
switch (receive_state)
{
case IDLE:
if (data_in == STX)
receive_state = RECEIVING;
break;
case RECEIVING:
if (data_in == LINEFEED) // End of string terminator found?
{
RxBuff[rxBuffPtr] = '\0'; // Terminate string
CheckForNewString();
receive_state = IDLE;
rxBuffPtr = 0;
}
else
{
// Only process readable characters
if ((data_in >= 0x20) && (data_in < 127))
{
if (RxBuffPtr < MAX_STR_LEN)
{
RxBuff[rxBuffPtr] = data_in;
rxBuffPtr++;
}
}
}
break;
}
}
void main()
{
StringBuffer[0] = 0; // Terminate string.
enable_interrupts(int_rda);
enable_interrupts(global);
while (TRUE)
{
if (new_string_received == TRUE)
printf("New string found: %s\n", StringBuffer);
}
}
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sean_tpc
Joined: 21 Aug 2008
Posts: 10
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| Posted: Fri Sep 26, 2008 4:20 pm |
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thank you so much guys....! |
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