We have a PN532 based product, and some of our units have been having troubles in the field. We have reasons to believe that this is due to poor antenna connection (our contact is not the most reliable).
We've implemented an antenna self test based on the user manual, but it has been hit or miss. It properly detects when the antenna is detached, but some times gives false negatives when re attached.
After reading the datasheet, we found that it says that this antenna test should only work for VBAT> 5 V, but in our design VBAT = 3.3 V. Is there a way to configure the self test to work with lower voltages?
Additionally, in the user manual says that a register value different from 0x00 means that the antenna is not detected, but in the datasheet it says that the only important bits are 7 and 6. Should I mask the result of the Diagnose command?
As you may already know the VBAT voltage can range from 2.7V to 5.5V. Nevertheless, as mentioned in the data-sheet, to guarantee this functionality, the VBAT is above 5V and the ambient temperature is between 0°C and 40°C.
Additionally, it is important to remember that it is needed to have the transmitter generating some RF in the antenna so that this can work properly.
Answering to your last question, andet_up bit in andet_control register is the one in charge of notifying if the antenna and/or the tuning network are not connected. For more information, please refer to chapter 8.6.9 of the data-sheet: