The system clock (SCLK) input is used to clock the internal shift register of the TIC12400-Q1. The SI data is latched into the input shift register on the falling edge of the SCLK signal. The SO pin shifts the device stored information out on the rising edge of SCLK. The SO data is available for the microcontroller to read on the falling edge of SCLK.

False clocking of the shift register must be avoided to ensure validity of data and it is essential the SCLK pin be in a logic LOW state whenever CS makes any transition. Therefore, it is recommended that the SCLK pin gets pulled to a logic LOW state as long as the device is not accessed and CS is in a logic HIGH state. When the CS is in a logic HIGH state, any signal on the SCLK and SI pins will be ignored and the SO pin remains as a high impedance output. Refer to Figure 8-22 and Figure 8-23 for examples of typical SPI read and write sequence.