f06x_smbus_slave.c

This example demonstrates how the C8051F06x SMBus interface can communicate // with a 256 byte I2C

   P0MDOUT = 0x00;                     // All P0 pins open-drain output

   P1MDOUT |= 0x40;                    // Make the LED (P1.6) a push-pull
                                       // output

   XBR0 = 0x01;                        // Enable SMBus on the crossbar
   XBR2 = 0x40;                        // Enable crossbar and weak pull-ups

   P0 = 0xFF;

   SFRPAGE = SFRPAGE_SAVE;             // Restore SFR page detector
}

//-----------------------------------------------------------------------------
// SMBus_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// The SMBus peripheral is configured as follows:
// - SMBus enabled
// - Assert Acknowledge low (AA bit = 1b)
// - Free and SCL low timeout detection enabled
//
void SMBus_Init (void)
{
   char SFRPAGE_SAVE = SFRPAGE;        // Save Current SFR page

   SFRPAGE = SMB0_PAGE;

   SMB0CN = 0x07;                      // Assert Acknowledge low (AA bit = 1b);
                                       // Enable SMBus Free timeout detect;
                                       // Enable SCL low timeout detect

   // SMBus clock rate (derived approximation from the Tlow and Thigh equations
   // in the SMB0CR register description)
   SMB0CR = 257 - (SYSCLK / (2 * SMB_FREQUENCY));

   SMB0ADR = MY_ADDR;                  // Set own slave address.

   SMB0CN |= 0x40;                     // Enable SMBus;

   SFRPAGE = SFRPAGE_SAVE;             // Restore SFR page detector
}

//-----------------------------------------------------------------------------
// Timer4_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// Timer4 configured for use by the SMBus low timeout detect feature as
// follows:
// - Timer4 in auto-reload mode
// - SYSCLK/12 as Timer4 clock source
// - Timer4 reload registers loaded for a 25ms overflow period
// - Timer4 pre-loaded to overflow after 25ms
// - Timer4 enabled
//
void Timer4_Init (void)
{
   char SFRPAGE_SAVE = SFRPAGE;        // Save Current SFR page

   SFRPAGE = TMR4_PAGE;

   TMR4CN = 0x00;                      // Timer4 external enable off;
                                       // Timer4 in timer mode;
                                       // Timer4 in auto-reload mode

   TMR4CF = 0x00;                      // Timer4 uses SYSCLK/12
                                       // Timer4 output not available
                                       // Timer4 counts up

   RCAP4 = -(SYSCLK/12/40);            // Timer4 configured to overflow after
   TMR4 = RCAP4;                       // ~25ms (for SMBus low timeout detect)

   EIE2 |= 0x04;                       // Timer4 interrupt enable
   TR4 = 1;                            // Start Timer4

   SFRPAGE = SFRPAGE_SAVE;             // Restore SFR page detector
}

//-----------------------------------------------------------------------------
// Interrupt Service Routines
//-----------------------------------------------------------------------------

//-----------------------------------------------------------------------------
// SMBus Interrupt Service Routine (ISR)
//-----------------------------------------------------------------------------
//
// SMBus ISR state machine
// - Slave only implementation - no master states defined
// - All incoming data is written to global variable <SMB_DATA>
// - All outgoing data is read from global variable <SMB_DATA>
//
void SMBUS_ISR (void) interrupt 7
{
   bit FAIL = 0;                       // Used by the ISR to flag failed
                                       // transfers

   // Status code for the SMBus (SMB0STA register)
   switch (SMB0STA)
   {
      // Slave Receiver: Slave address + WRITE received.  ACK transmitted.
      // Fall through.
      case SMB_SROADACK:

      // Slave Receiver: General call address received.  ACK transmitted.
      case SMB_SRGADACK:

         break;

      // Slave Receiver: Data byte received after addressed by general
      // call address + WRITE.
      // ACK transmitted.  Fall through.
      case SMB_SRGDBACK:

      // Slave Receiver: Data byte received after addressed by own
      // slave address + WRITE.
      // ACK transmitted.
      case SMB_SRODBACK:

         SMB_DATA = SMB0DAT;           // Store incoming data
         DATA_READY = 1;               // Indicate new data received

         break;

      // Slave Receiver: Data byte received while addressed as slave.
      // NACK transmitted. Should not occur since AA will not be cleared
      // as slave.  Fall through to next state.
      case SMB_SRODBNACK:

      // Slave Receiver: Data byte received while addressed by general call.
      //  NACK transmitted.
      // Should not occur since AA will not be cleared as slave.
      case SMB_SRGDBNACK:
         AA = 1;

         break;

      // Slave Receiver: STOP or repeated START received while addressed as
      // slave.
      case SMB_SRSTOP:

         break;

      // Slave Transmitter: Own slave address + READ received.  ACK
      // transmitted.
      // Load SMB0DAT with data to be output.
      case SMB_STOADACK:
         SMB0DAT = SMB_DATA;

         break;

      // Slave Transmitter: Data byte transmitted.  ACK received.  Fall
      // through.
      case SMB_STDBACK:

      // Slave Transmitter: Data byte transmitted.  NACK received. Fall
      // through.
      case SMB_STDBNACK:

      // Slave Transmitter: Last data byte transmitted.  ACK received.
      // No action necessary.
      case SMB_STDBLAST:

         break;

      // All other status codes invalid.  Reset communication.
      default:
         FAIL = 1;

         break;

   }

   if (FAIL)                           // If the transfer failed,
   {
      SMB0CN &= ~0x40;                 // Reset communication
      SMB0CN |= 0x40;
      STA = 0;
      STO = 0;
      AA = 1;

      FAIL = 0;
   }

   SI = 0;                             // Clear interrupt flag
}

//-----------------------------------------------------------------------------
// Timer4 Interrupt Service Routine (ISR)
//-----------------------------------------------------------------------------
//
// A Timer4 interrupt indicates an SMBus SCL low timeout.
// The SMBus is disabled and re-enabled if a timeout occurs.
//
void Timer4_ISR (void) interrupt 16
{
   char SFRPAGE_SAVE = SFRPAGE;        // Save Current SFR page

   SFRPAGE = SMB0_PAGE;

   SMB0CN &= ~0x40;                    // Disable SMBus
   SMB0CN |= 0x40;                     // Re-enable SMBus

   SFRPAGE = SFRPAGE_SAVE;             // Switch back to the Timer4 SFRPAGE

   TF4 = 0;                            // Clear Timer4 interrupt-pending flag
}

//-----------------------------------------------------------------------------
// End Of File
//-----------------------------------------------------------------------------