Figure 8-17 defines the format of the command and data transimission. There are four states in one frame.

• IDLE: SCLK is always existent and continuous, and DIN is always HIGH.
• START: DIN changes from HIGH to LOW after the IDLE states.
• DATA:
  • Head_bytes: command identifier that contains one 16-bit data and one check bit. It can be WRITE COMMAND ID or READ COMMAND ID (see Register Maps for more details).
  • Data_bytes_N: The N^th data-bytes, contains 3 × 17-bit data, each 17-bit data contains one 16-bit data and one check bit. N is the number of devices cascaded in a data chain.
• END: the device recognizes continuous 18-bit HIGH on DIN, then returns to IDLE state.
• CHECK BIT: the check bit (17^th bit) value is the NOT of 16^th bit value, to avoid continuous 18-bit HIGH (to distinguish with END).

Figure 8-17 CCSI Frame

The IDLE state is not the necessary, that means the START state of next frame can connect to the END state of current frame.