SLAZ372Q October   2012  – May 2021 MSP430FG479

 

  1. 1Functional Advisories
  2. 2Preprogrammed Software Advisories
  3. 3Debug Only Advisories
  4. 4Fixed by Compiler Advisories
  5. 5Nomenclature, Package Symbolization, and Revision Identification
    1. 5.1 Device Nomenclature
    2. 5.2 Package Markings
      1.      ZQW113
      2.      PN80
      3.      ZCA113
    3. 5.3 Memory-Mapped Hardware Revision (TLV Structure)
  6. 6Advisory Descriptions
    1. 6.1  CPU4
    2. 6.2  CPU19
    3. 6.3  EEM20
    4. 6.4  FLASH19
    5. 6.5  FLASH24
    6. 6.6  FLASH27
    7. 6.7  FLL3
    8. 6.8  FLL6
    9. 6.9  JTAG23
    10. 6.10 LCDA5
    11. 6.11 LCDA7
    12. 6.12 SDA6
    13. 6.13 TA12
    14. 6.14 TA16
    15. 6.15 TA21
    16. 6.16 TAB22
    17. 6.17 TB2
    18. 6.18 TB16
    19. 6.19 TB24
    20. 6.20 USCI20
    21. 6.21 USCI22
    22. 6.22 USCI23
    23. 6.23 USCI24
    24. 6.24 USCI25
    25. 6.25 USCI26
    26. 6.26 USCI28
    27. 6.27 USCI30
    28. 6.28 USCI34
    29. 6.29 USCI35
    30. 6.30 USCI40
    31. 6.31 XOSC5
    32. 6.32 XOSC8
    33. 6.33 XOSC9
  7. 7Revision History

USCI30

USCI Module

Category

Functional

Function

I2C mode master receiver / slave receiver

Description

When the USCI I2C module is configured as a receiver (master or slave), it performs a double-buffered receive operation. In a transaction of two bytes, once the first byte is moved from the receive shift register to the receive buffer the byte is acknowledged and the state machine allows the reception of the next byte.

If the receive buffer has not been cleared of its contents by reading the UCBxRXBUF register while the 7th bit of the following data byte is being received, an error condition may occur on the I2C bus. Depending on the USCI configuration the following may occur:

1) If the USCI is configured as an I2C master receiver, an unintentional repeated start condition can be triggered or the master switches into an idle state (I2C communication aborted). The reception of the current data byte is not successful in this case.
2) If the USCI is configured as I2C slave receiver, the slave can switch to an idle state stalling I2C communication. The reception of the current data byte is not successful in this case. The USCI I2C state machine will notify the master of the aborted reception with a NACK.

Note that the error condition described above occurs only within a limited window of the 7th bit of the current byte being received. If the receive buffer is read outside of this window (before or after), then the error condition will not occur.

Workaround

a) The error condition can be avoided altogether by servicing the UCBxRXIFG in a timely manner. This can be done by (a) servicing the interrupt and ensuring UCBxRXBUF is read promptly or (b) Using the DMA to automatically read bytes from receive buffer upon UCBxRXIFG being set.

OR

b) In case the receive buffer cannot be read out in time, test the I2C clock line before the UCBxRXBUF is read out to ensure that the critical window has elapsed. This is done by checking if the clock line low status indicator bit UCSCLLOW is set for atleast three USCI bit clock cycles i.e. 3 X t(BitClock).

Note that the last byte of the transaction must be read directly from UCBxRXBUF. For all other bytes follow the workaround:

Code flow for workaround

(1) Enter RX ISR for reading receiving bytes
(2) Check if UCSCLLOW.UCBxSTAT == 1
(3) If no, repeat step 2 until set
(4) If yes, repeat step 2 for a time period > 3 x t (BitClock) where t (BitClock) = 1/ f (BitClock)
(5) If window of 3 x t(BitClock) cycles has elapsed, it is safe to read UCBxRXBUF