SPI Write operation is used to send data from the controller device to the peripheral device. SPI write can be a single byte write as shown in Figure 7-7 or burst write as shown in Figure 7-8 where multiple bytes can be written to the device. The operation is performed over the SPI bus, where the controller device drives CS low, generates the serial clock (SCLK) and sends data to the peripheral. SPI Write is commonly used to configure peripherals, send control commands, or transfer data. During a SPI single write, the device sends the last data from the register indicated by the register pointer. On a SPI burst write, the address is automatically incremented and the device sends the last data from the updated register pointer.

Figure 7-7 SPI Single Write

Figure 7-8 SPI Burst Write

SPI Write Steps

1. Drive CS low. This enables the internal shift register.
2. Shift 24 bits of data into the device in a MSB first fashion, MSB bit . Data must be stable during the rising edge of SCLK.
3. The MSB bit must be a '0' indicating it is a write operation.
4. On the SDO pin, the device sends the first 2 bits as 2’b11 (indicating it to be a status segment). followed by 6 bits are the Bit 5 to 0 of the Fault status register. The next 8 bits are all 0s followed by 8-bit current data in the register selected by register pointer.
5. After the last bit of data is transferred, drive SCLK low if there is no more data to be transferred.
6. The previous content of the register is sent out on SDO as the data byte is driven on SDI.
7. De-assert CS (drive it high) to end the write cycle.