I2C IBSR_IBB clearing early

sricker — Thu, 24 May 2007 00:49:14 GMT

CW Pro v4.6

9S12DT256, mask 0L01Y

What would cause the IBB bit in IBSR to clear in the middle of a byte being transmitted?

I am trying to write to and then read and expansion port chip. I had been writing successfully but when I started to do the reads I noticed that my I2C bean function CheckBus() which is a macro for IBSR_IBB is clearing in the middle of a byte being transmitted. Because the RecvBlock function takes a pointer to a buffer I was calling that function and then trying to wait for the indication that a specified number of bytes had been received.

I need to write to the expansion port chip one byte address with write bit set and the number of the register to read as the second byte. Then I need to send the one byte address with write bit cleared (which RecvBlock() does) prior to receiving the number of bytes specified as a parameter to RecvBlock().

Here is the code:

   byte error ;
   byte receivedData[4];
   word *bytesRead ;
   destination = port ;

   error = I2C1_SelectSlave( (byte)(destination + ADDRESS_BASE) );

   IICCommand.asField.commandByte = INPUT_PORT_REGISTER ;

   error = I2C1_SendChar(IICCommand.asField.commandByte);

   // blocking while bus is busy
   while(IBSR & IBSR_IBB) // or while(I2C1_CheckBus())
      PORTE |= 0x04 ;           // for debugging with scope
   PORTE &= ~0x04;

   error = I2C1_RecvBlock(receivedData, 1, bytesRead);

   while(IBSR & IBSR_IBB)
         PORTE |= 0x04 ;
   PORTE &= ~0x04;

   *data = receivedData[0] ;   // *data is a parameter to this function

I have put a scope on SCL, SDA and on GPIO PE2 and watched this happen over and over. IBB should go high on a start condition and low on a stop condition and indicate a busy bus.

Re: I2C IBSR_IBB clearing early

NLFSJ — Sat, 09 Jun 2007 21:47:19 GMT

Hi Shawn,

A loss of arbitration, please read the IIC Phillips spec under LOAs. When there is a loss of arbritation the Master defaults to a Slave and the IBB and other control bits are cleared. To minimize that problem please have the implement IIC pullup accelarators. Such devices can be found on www.google.com http://forums.freescale.com/freescale/board/www.google.com.

I hope this helps.

Regards,

Nina

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I2C IBSR_IBB clearing early

Re: I2C IBSR_IBB clearing early