NFCT receives incomplete byte on SLP_REQ

[Remo]

Hi all

I'm using the NFCT peripheral of the nRF52832 Revision 1 and I'm facing the following issue:

When the reader sends the SLP_REQ, the NFCT receives an incomplete amount of bytes.
This means that after the RXFRAMEEND event occurred, the RXD_AMOUNT register is 0x22 -> 4 bytes and 2 bits.

The reader sends the frame correctly (0x50, 0x00, 0x57, 0xCD) and the NFCT doesn't signal a CRC error:
FRAMESTATUS_RX = 0x00 and RXD_FRAMECONFIG = 0x15.

The receive buffer contains: 0x50, 0x00, 0x57, 0x9A, 0x01.

Why are 2 additional bits signaled? Do you know this issue?

Many thanks for your help.

Best regards

[bjorn-spockeli]

Hi Remo, 

Which SDK version are you using?

I have not seen this issue before and I can see any erratas covering what you're describing so I will have to forward this internally. Will keep you posted. 

Best regards
Bjørn

[Remo]

Hi Bjørn

I used SDK V15.0.0 as reference, but I'm writing my own driver.

Best regards

[bjorn-spockeli]

Hi Remo, 

I discussed this with R&D and they said that a SLP_REQ is handled by the NFCT hardware without any SW intervention. Since the NFCT is entering the sleep state, they said that the data in the RX buffer could be unreliable. 

Bjørn

[Remo]

Hi Bjørn

When I received a frame, the first thing I did was to check that a complete amount of bytes was received. And afterwards I checked which command has been sent from the reader. Seems that I have to soften the length check in case of the SLP_REQ.

Thank you very much for the clarification.

Best regards