8.1 Startup Initialization

By default, the ATA6847 starts with the watchdog enabled. It is necessary to follow the start-up procedure to enter a normal operation or to reconfigure the watchdog.

As soon as the microcontroller output voltage rises up to the valid operating range, the ATA6847 transitions to Standby mode and deasserts the NRES pin. By default, the WDT starts in Time-out mode. The first microcontroller must trigger the watchdog within the long open window (tLW).

After the first watchdog trigger, the ATA6847 is ready for configuration via SPI. The application should follow the following start-up sequence:

  • Once the microcontroller SPI has been initialized, a valid WDT trigger sequence must be sent to the ATA6847 (WDTRIG = 0x55).
  • The watchdog must be configured according to application requirements.
  • The remaining ATA6847 configuration registers must be set according to application requirements.
Figure 8-1. ATA6847 Simplified Start-up Procedure