The SPI is used to set device configurations, operating parameters, and read out diagnostic information. The SPI operates in slave mode. The SPI input-data (SDI) word consists of a 16-bit word, with 8 bits command and 8 bits of data. The SPI output data (SDO) word consists of 8 bits of status register with fault status indication and 8 bits of register data. Figure 7-22 shows the data sequence between the MCU and the SPI slave driver.
Figure 7-22 SPI Transaction Between MCU and the device
A valid frame must meet the following conditions:
- The SCLK pin must be low when the nSCS pin goes low and when the nSCS pin goes high.
- The nSCS pin should be taken high for at least 500 ns between frames.
- When the nSCS pin is asserted high, any signals at the SCLK and SDI pins are ignored, and the SDO pin is in the high-impedance state (Hi-Z).
- Full 16 SCLK cycles must occur.
- Data is captured on the falling edge of the clock and data is driven on the rising edge of the clock.
- The most-significant bit (MSB) is shifted in and out first.
- If the data word sent to SDI pin is less than 16 bits or more than 16 bits, a frame error occurs and the data word is ignored.
- For a write command, the existing data in the register being written to is shifted out on the SDO pin following the 8-bit command data.