It can be useful to know when the PN532 is transmitting or receiving. For better oscilloscope sync. or to debug timings in applications. For this, you can try to use the `CIU_AnalogTest` with its AUX1 and AUX2 output. ## `CIU_AnalogTest` register (address 6328h) > See PN532/C1 § 8.6.23.53  It includes 2 symbols to control the pins AUX1 and AUX2: - `AnalogSelAux1[3:0]` for the AUX1 output - `AnalogSelAux2[3:0]` for the AUX2 output ## Register configuration  By pushing `0b11001101` in the `PN53X_REG_CIU_AnalogTest` register, we have: - `0b1100` in `AnalogSelAux1[3:0]`, TxActive on AUX1 - `0b1101` in `AnalogSelAux2[3:0]`, RxActive on AUX2 Code with `kpn532` library: ```cpp pNFC->WriteRegister(PN53X_REG_CIU_AnalogTest, 0b11001101); ``` ## Capture  In this example we: - Send `InCommunicateThru` command with `0x06 0x00` data (`ST25TB - Initiate`)  - Wait interrupt, then Read ACK  - _NFC exchange is done now_  - AUX1 is high when transmitting - AUX2 is high when receiving This is confirmed with an oscilloscope capture  - Wait interrupt, then Read `InCommunicateThru` response with `0x00 0x89` data (status code: `0x00`, `ST25TB - chipid: 0x89`)  ### Timings The NFC exchange is ~1.4 ms (`P0`), but the whole communication part is ~3.3 ms (`P1`).  ## References ### NXP PN532 - https://www.nxp.com/products/rfid-nfc/nfc-hf/nfc-readers/nfc-integrated-solution:PN5321A3HN - https://www.nxp.com/docs/en/nxp/data-sheets/PN532_C1.pdf - https://www.nxp.com/docs/en/user-guide/141520.pdf ### Library & Analyzer - https://github.com/BdF-LabSec/kpn532 - https://github.com/gentilkiwi/Saleae-Logic2-HLA-NXP-PN532