The sleep wake error (SWE) timer is a timer used to determine if specific external and internal functions are working. Figure 10-22 provides an overview of when SWE timer is on and starts or off when fail-safe mode is enabled. Upon power up, POR or UVSUP event, the SWE timer starts, tINACTIVE, which the processor has to configure theTCAN114x-Q1, clear the PWRON flag or configure the device for normal or listen mode before the SWE timer expires. This feature cannot be disabled for power up. If the device has not had the PWRON flag cleared or been placed into normal or listen mode, it enters sleep mode. The SWE timer can be disabled for the other scenarios that causes the device to enter fail-safe mode by setting SWE_DIS; 8'h1C = 1 and FS_DIS at 8'h17 = 1.
The device wakes up for a CAN bus WUP or a local wake thus entering standby mode. Once in standby mode, the tSILENCE and tINACTIVE timers start. If tINACTIVE expires, the device re-enters sleep mode. When the device receives a CANINT, LWU or FRAME_OVF such that the device leaves sleep mode and enters standby mode, the processor has until tINACTIVE expires to clear the flags and place the device into normal mode. If this does not happen, the device enters sleep mode. When in standby, normal or listen mode and tSILENCE (SWE_DIS=1) or CANSLNT (SWE_DIS=0) persists for tINACTIVE, the device enters sleep mode. Examples of events that could create this are the processor is no longer working and not able to exercise the SPI bus, a go to sleep command comes in and the processor is not able to receive it or is not able to respond.