NFC-V: quick notes
Here is some notes when I've been working on NFC recently. I hopes this will help someone who just like me being confused between NFC's generations and standards.
A NFC tag is a chip inside a NFC card. Dynamic NFC tag is a chip that can communicate with MCU. A NFC reader is a chip that read tags, and sometimes comunicate with other reader, which is called NFC Emulators. Some types of cards are emu-able, some are not.
NDEF is a standard on top of NFC-A, NFC-B, and NFC-F. It’s a nice protocol standdard but if you’ve got a ST25DV, it cannot be used with NDEF. ST25DV follow ISO15693 standard (or NFC-V).
On Android, to comunicate with NFC-V tags, use nfc-v tranceive(), with the input is raw ISO15693 bytes.
The feeling of being elite while calling something by its standard instead of name
You can’t affort to by ISO15693 standard? No worries, stick to the chip’s datasheet/manual, here is my example with ST25DV. In section 7.4, all (maybe) ISO15693 commands are listed there, follow some custom (vendor) commands.
ST25DV’s default password is 00000000 - 8 bytes of zeros. To open a security session, use Present Password command. To close one, present a wrong password.
ISO15693 define the length of Read/Write Messages is the length actually transferred = the length that you put in raw message + 1. And the maximum data length to be transferred is 256. But 256 won’t fit in a byte. So that is why the length that you put in raw message is subtracted by one.
When using react-native-nfc-manager, call requestTechnology() once, then doing the tranceive as much time as you want. I’ve been struggling of failing requestTechnology() while calling it multiple times.
Some NFC tag claim to be dynamic but it lack of SRAM section to comunicate between a reader and MCU such as M24LR. It is a dynamic tag, but frequently writing to EEPROM is not a good choice. Imagine your product broke after 1000 uses. That is why ST25DV came to replace M24LR. It has a section of memory call FTM. This can be used to transfer messages between MCU and readers.
I’ve been using this to transfer bitmaps to an epaper diplay. Some initial thought that it would need a MCU with big size of SRAM to carry bitmaps for the display. But why we store bitmaps on MCU while we pass every messages on NFC tags to the display?