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code stuck at I2C_WRITE() ??

 
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ye



Joined: 11 May 2005
Posts: 57
Location: london

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code stuck at I2C_WRITE() ??
PostPosted: Tue Dec 13, 2005 6:35 am     Reply with quote
Hi all,

The following code is a pretty simple EEPROM test code. It works on one of my test board but doesn't on another one. Can anybody think of any problems in software or hardware for this one?

Code:
#include<18f8722.h>

#fuses HS, LVP, NOWDT

#use delay(clock=24000000)


#use i2c( Master, fast, SDA = PIN_C1, SCL = PIN_C0)


#define EEPROM_WRITE    0b10100000        // bit 7 - 4 are the control bits where '1010' means either WRITE or READ operation
#define EEPROM_READ     0b10100001        // bit 3, bit 2 and bit 1 together represent the device address which is 000 here




void I2C_Init( void )
{
   output_float( PIN_C0 );
   output_float( PIN_C1 );


}



int1 I2C_Device_Ready( void )
{
   int1 ACK;
   i2c_start();

   ACK = i2c_write( EEPROM_WRITE);

   i2c_stop();
   return !ACK;
}



void I2C_Device_Write( signed int *EEPROM_Buffer, int EEPROM_Address_MSB, int EEPROM_Address_LSB, int Buffer_Length)
{
   int i;

   while( !I2C_Device_Ready() );  // Wait for ready
   i2c_start();
   i2c_write( EEPROM_WRITE );         // Send control byte
   i2c_write( EEPROM_Address_MSB );   // Send most significant address byte
   i2c_write( EEPROM_Address_LSB );   // Send least significant address byte
   
   for( i=0; i<Buffer_Length; i++)
       i2c_write( *(EEPROM_Buffer + i) );
 

   i2c_stop();
}




void I2C_Device_Read( signed int *EEPROM_Buffer, int EEPROM_Address_MSB, int EEPROM_Address_LSB, int Buffer_Length)
{
   int i;

   while( !I2C_Device_Ready() );  // Wait for ready
   i2c_start();
   i2c_write( EEPROM_WRITE);
   i2c_write( EEPROM_Address_MSB );   // Send most significant address byte
   i2c_write( EEPROM_Address_LSB );   // Send least significant address byte
   i2c_start();
   i2c_write( EEPROM_READ);

   for( i=0; i< Buffer_Length - 1 ; i++)
       *(EEPROM_Buffer + i) = i2c_read();
 
   *(EEPROM_Buffer + (Buffer_Length - 1) ) = i2c_read(0);  // no ACK for the last byte
   i2c_stop();
}




void main()
{

   I2C_Init();


   while( !I2C_Device_Ready() )
      ;

   while(1)
   {
      output_high(pin_f5);
      delay_ms(500);
      output_low(pin_f5);
      delay_ms(500);
   }   




}






I realise on the second board, the code couldn't run through function I2C_Device_Ready() and actually got stuck at I2C_WRITE() (I did some simple test on it and sure about this thing). The most weird thing is, I couldn't even see any signal coming out of the PIC at PIN A1 or A0 on oscillope. So I think this problem has nothing to do with external circuitry because it's the PIC that fails to send signal out on SDA. But why???
ye



Joined: 11 May 2005
Posts: 57
Location: london

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PostPosted: Tue Dec 13, 2005 7:19 am     Reply with quote
actually i figured out the problem.

forgot to connect pull up resistors... Embarassed
Ttelmah
Guest
PostPosted: Tue Dec 13, 2005 7:28 am     Reply with quote
Obvious question. Have you got resistive pull-ups on the lines?. For I2C, the PIC only pulls the signal down. It is up to the external circuit to pull the lines up. Without the pull ups, there will be no activity on the lines, and the code will not work.

Best Wishes
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