根据Reference Manual,Inter-IC Sound (I2S) bus specification from PhilipsSemico nductors (February 1986, Revised June 5, 1996). 关于具体的定义你也可以参考我们的Application Note
http://cache.freescale.com/files/dsp/doc/app_note/AN1848.pdf
chapter4.3 I2S, LEFT-JUSTIFIED, AND EIAJ (RIGHT JUSTIFIED) FORMATS