Revision Information:
Note: This applies only when C functions are used to call the ASM library.
Due to a change in C calling conventions by IAR the USI I2C library has been modified and two seperate revisions - A and B are provided in order that they are compatible with all IAR versions. 

For IAR Version1, during a C function call, the first parameter passed as an argument is assigned to R12 or R13:R12, depending on the size of the parameter. The second argument is passed in R14 or R15:R14. Should there be no more available registers, the parameter is passed on the stack.
For IAR Version2, the first parameter is assigned the first free register, starting from R12.
Please refer to the MSP430 C/C++ Compiler Reference Guide for a detailed description of the calling convention changes(available in 'Help' tab of IAR Embedded Workbench).

The USI I2C Library Rev. A works with IAR Version 1 (upto and including IAR V3.42A)
The USI I2C Library Rev. B  has been modified to work for all later versions of IAR.
Please go to Help -> About -> Product Info  to determine your IAR version.
Note that only the source files have changed between revisions, the same example files can be used across both revs.