2.6 Considering Reset Behavior

For the reset behavior, two states must be distinguished. The first one is that the device is in the OFF state. In this case, the device will not react to a reset and stays in the OFF mode. In the second state, the device is active. This happens if any wake conditions were triggered in the past and no reset or OFF mode instruction was triggered. The Microchip ATA UHF products can be set or kept in the Reset state in three different ways. Power-on-Reset (POR), External Reset (NRESET) and the Watchdog Reset (WDR) are available. The source that triggers the reset is available in the MCUSR register and, after the reset, the device will temporarily stay awake. During the system initialization, the firmware checks if a valid wake source is available or not. If the wake source is unavailable, the device is set to the OFF mode. If the application is reset, the device is not responsive to the main μC because no wake source is available after a reset. For a robust application, it is essential for the main µC to detect a reset of the ATA UHF product. For the NRESET as reset source, the main µC is the initiator of the event, which means it is a known event. The situation is similar if a POR reset happens. The main µC must be able to detect this event.

The situation becomes difficult in the case of a WDR. Without a valid wake source, the main μC is not aware of this reset and the subsequent OFF mode. In this situation, the main µC and the ATA UHF device are not synchronized because the main µC does not detect the WDR event. Use the OFF mode behavior of the wake pins to identify the WDR. In the OFF mode, all the I/O pins, except for the one with wake capability and NRESET, will be in tri-state. NPWRONx pins and NRESET are pulled to high level in the OFF mode. For example, configure the PC1 at a low level during normal operation, and a high transition indicates the OFF mode. The main µC can detect this.