NTAG I2C plus keeps sending only NACKs

[donwasabi]

Hi :smileyhappy:,

My NXP NTAG I2C plus keeps sending NACKs as confirmation after every sent byte, starting with the addressing of the device and i don't know why :smileysad: (it worked like a charm a while ago). I tested another NTAG device, same behavior. The address was not modified, so it should be the original b1010101 (0x55 hex or 85 in decimal), so the shifted address seems to look right for the WRITE command (170 dec = 1010101(0)). Maybe someone encountered a similar behaviour?

[donwasabi · Accepted solution]

Found the problem:

The VCC was not correctly connected, so reading/writing from NFC side was possible, because it harvested the energy from the NFC field, but communicating over i2c was not possible because the lack of power.