CCS/UCD3138064A: when 35 & 36pin work in I2C mode, many of the bit fields are not used. Can you explain what fields are not used ?

Basically, the I2C module is a PMBus module with 3 things removed:

1.  slave mode support

2. Alert line

3. Control line

Also, the PMBus hardware in master mode automatically inserts the byte with number of bytes in it into block messages.  This is not compatible with I2C, so it is removed from the I2C module.  So the bits removed are fairly obvious, but here is the list:

PMBST or I2CST bits removed
  Bit 19: CONTROL_RAW
  Bit 18: ALERT_RAW
  Bit 17: CONTROL_EDGE
  Bit 16: ALERT_EDGE
  Bit 11: RPT_START
PMBINTM or I2CINTM - bits removed
  Bit 7: CONTROL
  Bit 6: ALERT
PMBCTRL2, PMBHSA – all removed, only deals with slave mode
PMBCTRL3 or I2CCTRL3 – bits removed
  Bit 21: SLAVE_EN
  Bit 11: CNTL_DIR
  Bit 10: CNTL_VALUE
  Bit 9: CNTL_MODE
  Bit 8: ALERT_DIR
  Bit 7: ALERT_VALUE
  Bit 6: ALERT_MODE
  Bit 5: CNTL_INT_EDGE
PMBCTRL3 or I2CCTRL3 – notes
  Bit 23: I2C_MODE_EN – present, but I2C is always enabled regardless of setting
  Bit 22: MASTER_EN – present, needs to be set for master to work

This only affects the I2C interface, not anything else.