Send messages above 255 bytes with CR95HF

[DCarv]

Hi,

I'm using CR95HF to comunicate with a ST25DV.

I want to write/read the ST25DV mailbox of 256 bytes but the CR95 dont allow.

I've been looking in the source code of the CR95HF demo board and found a patch command to increase the buffer.

After that if I use the command 0x24 instead the 0x04 (SendRecv) it is possible to send more than 255 bytes.

Incredibly I have not found any documentation that explains this patch and how the new commands work.

Where I can get that information?

Thanks

[Brian TIDAL]

Hi,

This patch is only provided for demo purpose as part of the Discovery kit for CR95HF Reader & M24LR04E. It enables sending of data exceeding the 1-byte length limit using a mechanism similar to the one used for long frame support in receive mode. This patch is not officially supported and is not included in the x-cube-nfc3 library. It is not recommended to use this patch in customer application.

Regarding the ST25DV Write Message, segmentation of data is needed as soon as you need to send any buffer bigger that the mailbox size. Therefore I would recommend to implemented a segmentation mechanism taking into account the size of the mailbox and the maximum size of data supported by the reader.

Feel free to share more details regarding your application such as the reason why you need to write a full 256 bytes message.

Rgds

BT

[DCarv]

If there is a way around this limitation of the CR95HF, I dont understand why it is not officially supported.

ST made a NFC tag with 256 bytes of fast transfer buffer, and then the writer device can not write the entire memory.

I still have to make the segmentation of data, but I prefer to send the smallest number of blocks.

Regards

[Brian TIDAL · Accepted solution]

​Hi,

ST25R3911B and ST25R3916 readers fully support ST25DV Write Message and Fast Write Message commands with up to 256 bytes message data.

ST25R95/CR95HF reader is anterior to ST25DV. it behaves as designed with a 1-byte length limit.

As for most implementations, a segmentation mechanism is needed to handle mailbox messages bigger than 256 bytes, the ST25R95/CR95HF 1-byte length limit should not be an issue.

Rgds

BT