Extract only part of the card or tag data

You can extract parts of the card or tag data, or choose to send UID, NDEF records or block data, by setting values in config.txt.

There are three types of data you might want to extract from a card or tag:

UID - The unique identifier of the card/tag. This is typically either 4 or 7 bytes of data (32 or 56 bits). It is usually stored in a fixed location within the first block of the card or tag's memory depending on tag type.
NDEF - A stream of NDEF (NFC Data Exchange Format) records encoded and stored in the card or tag's memory area according to the NFC Forum specification for the tag type. Extracted by NDEF record type or ID.
Block data - A sequence of up to 16 bytes of data (or 255 bytes for NFC Type 5) stored in a particular location in the card or tag's memory area and accessed directly by specifying the block number, offset and length within the block.

The simplest situation is to set NFCType#=U or MIFAREClassic=U to send the whole UID or NFCType#=N to send all NDEF records.

To extract part of the block data you need NFCType=B or MIFAREClassic=B, then identify which data block to read, using settings with a TagRead prefix.

The following example extracts data in this way:

Example: Changes to config.txt to extract a fixed length of data from a particular start point

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!VTAPconfig

MIFAREClassic=B
TagReadBlockNum=8
TagReadKey=123ABC456DEF
TagReadKeyType=B
TagReadOffset=5
TagReadLength=4
TagReadFormat=d

Here you specify which block to read (with the key and key type to use, if needed), the offset within the block to start taking data, counting from 0, and the length of data to take. The output format is set to 'd'ecimal. So, in this case:

Extracting data to send based on separators, sections and character counting