ST25 as a serial communications bridge?

[LHell.1]

Hi,

We wish to include the ST25DV64K in our product for two main reasons:

1. Most importantly: The electronics in our product will be completely sealed in by a potting mass, in order to ensure waterproofness. We need a way to establish a serial communications link between a PC and the microcontroller, which will be used both in the factory during production, and in testing, certification and for field diagnostics. As fas as I understand, the ST25's 256-byte high-speed buffer should be able to give us such a serial communications bridge over NFC or RFID. However, I have problems finding a proper off-the-shelf reader that would provide this in a plug-and-play manner. Ideally, I would buy an NFC or RFID reader that can be plugged into the USB port on a PC, and provide me with something similar to a PuTTY bi-directional serial communication stream. I would power on my product, place the reader up to its NFC antenna, and talk back and forth with the microcontroller. Does this exist? Is this not the entire point of the ST25's high-speed buffer?

2. Non-volatile memory for a post-mortem log. Would enable us to write a log of critical events that occur during operation and read this out from the device if it dies in the field (battery depleted or otherwise). As far as I understand we should be able to read out the 8 kB EEPROM using for instance an NFC-enabled phone, which simplifies gathering logs in the field. Is any specific app or anything required for this, or can any standard NFC-reading app be used?

[LHell.1]

An alternative may be to use for instance the X-NUCLEO-NFC05A1 devkit, if it is easy to set up a continuous serial streaming channel with the included example code. Would that work? I don't have time to do a lot of design on the reader side of things, and would ideally just buy something very plug-and-playey.

[JL. Lebon · Accepted solution]

​Hello,

First of all, thank you for considering the ST25DV64K for your design.

About your second question:

It is possible to read tag's memory content (EEPROM) without any appliaction from an NFC enabled Android phone or from an iPhone. This is what we call "native" reading. For this to work, the content of the memory must be formated in the specific NDEF file as defined in the NFC Forum specification, and also contains a propoer CCFile. Then, depending on the type of NDEF record contained in the NDEF file, the phone will automatically trigg some action upon tag detection (open a browser, open a message app, etc.).

Another possiblity is to read the content of the memory with a dedicated application. In that case, the memory doesn't need to be formated as a NDEF File, it can contain anything. Android and iOS automatically report the presence of a tag to the application level, then the application simply has to send NFC read commands to read the memory content.

About memory size that the phone can read, there is not really a limit to 8kbits.

If you want a "native" read (no dedicated application), then it depends on the phone you are using. With android version 9.0 and above and with iOS, memory size limit that can be natively read is 2Mbits. With Android version < 9.0, you are limited to 8kbits and tags with size > 8kbits will not work correctly (even if you use less than 8Kbits), so ST25DV04K is to be prefered over ST25DV64K.

Now if you go for a dedicated application to read the memory, again the limit is 2Mbits, whatever the android version.

So depending on which phone you want to use, and which size you need, you have to make a choice between native read and tag's memory size.

I will check if one of my collegue can answer your first question.

Best reagrds.

[Brian TIDAL]

Hi,

About your first question:

The ST25 Embedded NFC library provides a ready to run demo and an API to communicate between a reader and a MCU connected to a ST25DV through I2C (fast transfer mode). This can be run on for instance on X-NUCLEO-NFC05A1. See FTM demo inside the package. The demo uses the USB Virtual Comm Port for log purpose but it should be quite easy to reuse the USB Virtual Comm Port for serial communications between the PC and the reader.

Rgds

BT

[LHell.1]

Thank you for your input, I will try the NUCLEO solution.