configuration register
| CHLEN | Channel length (number of bits per audio channel) |
| DATLEN | Data length to be transferred |
| CKPOL | Inactive state clock polarity |
| I2SSTD | standard selection |
| PCMSYNC | PCM frame synchronization |
| I2SCFG | I2S configuration mode |
| SE2 | I2S enable |
| I2SMOD | I2S mode selection |