SLASF77A December 2022 – September 2023 AFE11612-SEP
PRODUCTION DATA
For systems that contain several devices, the SDO pin can be used to daisy-chain multiple devices together. This daisy-chain feature is useful in reducing the number of serial interface lines. The first CS falling edge starts the operation cycle. SCLK is continuously applied to the input shift register when CS is low.
If more than 24 clock pulses are applied, data ripple out of the shift register and appear on the SDO line. These data are clocked out on the SCLK rising edge and are valid on the falling edge. By connecting the SDO output of the first device to the SDI input of the next device in the chain, a multiple-device interface is constructed. Each device in the system requires 24 clock pulses. Therefore, the total number of clock cycles must equal 24N, where N is the total number of devices in the daisy chain. When the serial transfer to all devices is complete, CS is taken high. This action transfers data from the SPI shifter registers to the internal register of each device in the daisy-chain and prevents any further data from being clocked in. The serial clock can be continuous or gated. A continuous SCLK source can only be used if CS is held low for the correct number of clock cycles. In gated clock mode, a burst clock containing the exact number of clock cycles must be used and CS must be taken high after the final clock in order to latch the data. Figure 7-29 to Figure 7-32 illustrate the daisy-chain operation.