The TLC696xx-Q1 family support diagnostics features including the LED short detection (LSD), LED open detection (LOD) and thermal shutdown detection (TSD). As shown in Figure 3-3, the FC27 register records the current chip fault status and the FC26 register records the previous chip fault status including the chip index and the fault types. In the normal system without the additional TLC69699-Q1 device, the host controller needs to read the FC26 and FC27 register for the last LED driver device every frame to detect if there are any faults in the daisy chain if the host is not equipped with UART readback capability.

TLC69699-Q1 implements the fault interrupt pin to indicate multiple fault types in the system, including the DAISY_CHAIN_FAULT, which indicates one or multiple devices in the daisy chain report LOD, LSD and TSD errors. The host controller can detect the FAULT interrupt status of TLC69699-Q1 and read the FC26/FC27 register of the TLC696xx-Q1 to further locate the chip index and fault type. Mapping the DAISY_CHAIN_FAULT to fault interrupt signal can save additional time for reading FC26/27 every frame, which can help effectively reduce the CCSI frequency.

With the DAISY_CHAIN_FAULT interrupt feature, the time reserved for the fault polling can be removed. So the TCON can reduce the SPI frequency from 8MHz to 5.2MHz in this 43 piece cascaded case. The next section explains the setting of the SPI frequency in detail.