problem with twi (AT91SAM7X256)

spm · **Joined:** Tue Aug 24, 2010 4:12 pm **Posts:** 4

hello

i want to implement an image sensor that utilizes an I2C protocal to read/write the registers.

but i wasn't successful !

when i write registers, i see no change in the sensor status. also can't read register values!

i think the sensor doesn't answer the I2C!

i couldn't find any I2C sample code that checks ACK and NACK response.

can anyone help me to write a code to realize ACK from sensor?

this is my code:

Code:

// PIOA-pin setup:
   AT91F_TWI_CfgPIO();
   // clk enable:
   AT91F_TWI_CfgPMC();
   // TWI setup:
   AT91F_TWI_Configure(AT91C_BASE_TWI);   // Reset peripheral(SWRST) // Set Master mode(MSEN)
   // set TWI clk:
   *AT91C_TWI_CWGR = (1<<16)|(45<<8)|(45);

   *AT91C_TWI_MMR = 0x210100;
   *AT91C_TWI_IADR = 0x11;   //internal address
   
   *AT91C_TWI_CR = AT91C_TWI_START | AT91C_TWI_STOP | AT91C_TWI_MSEN;
   *AT91C_TWI_THR = 0xc0;
   
   status = *AT91C_TWI_SR;
   while(status & AT91C_TWI_NACK)
      status = *AT91C_TWI_SR;

   status = *AT91C_TWI_SR;
   while(!(status & AT91C_TWI_TXCOMP))
      status = *AT91C_TWI_SR;

i expect to have an infinite loop if the sensor doesn't ACK.

Code:

   status = *AT91C_TWI_SR;
   while(status & AT91C_TWI_NACK)
      status = *AT91C_TWI_SR;

but doesn't! even if i change the slave address !!

please help me
thanks

dfridley · **Joined:** Thu Feb 25, 2010 5:02 pm **Posts:** 88

Hello -

First thing I would check is, hook a scope to the TWD and TWCK lines (PA10, PA11) and verify they are changing when you send/recieve data...

If they are not changing (especially the clock) then the problem is in the configuration of the TWI.

Regards,

spm · **Joined:** Tue Aug 24, 2010 4:12 pm **Posts:** 4

thank you dfridley
but i haven't a scope now!

doubt to my code !
can you tell me is my code correct or not?
i just want a code to clarify if the sensor acknowledges after sending address?

dfridley · **Joined:** Thu Feb 25, 2010 5:02 pm **Posts:** 88

We will need more info...

Can you post the code for these two functions?

Quote:

Code:

// PIOA-pin setup:
   AT91F_TWI_CfgPIO();
   // clk enable:
   AT91F_TWI_CfgPMC();

Also, did this code come from the TWI example at the Atmel site?

Regards,

spm · **Joined:** Tue Aug 24, 2010 4:12 pm **Posts:** 4

these functions was declared in the lib_at91sam7x56.h from atmel (attached)

dfridley · **Joined:** Thu Feb 25, 2010 5:02 pm **Posts:** 88

Quote:

these functions was declared in the lib_at91sam7x56.h from atmel (attached)

Ok, that looks fine.

What about the hardware... Are there external pullups on the TWD and the TWCK lines?

Edit
Finally got a chance to take a closer look at your code.
You probably want to wait until the transmitter is ready (i.e. the data has been sent) before checking for the NACK.

Eg.

Code:

   // --snip--

   *AT91C_TWI_CR = AT91C_TWI_START | AT91C_TWI_STOP | AT91C_TWI_MSEN;
   *AT91C_TWI_THR = 0xc0;
   
   // Wait until the data is sent before checking for NACK or TXCOMP. 
   // See flowcharts section 25.9.6 in AT91SAM7X datasheet .
   do
   {
        status = *AT91C_TWI_SR;
   }
   while( !(status & AT91C_TWI_TXRDY) );

   status = *AT91C_TWI_SR;
   while(status & AT91C_TWI_NACK)
      status = *AT91C_TWI_SR;

   // --snip--

Regards,

problem with twi (AT91SAM7X256)

Who is online