This information is not required to program the NFC tag; you can just follow the steps outlined in Programming a tag. The following sections provide background information about how the tag data is stored in the Type 2 Tag.

The NFCT data is stored in RAM, in the same way as data for other nRF52 peripherals. The data format that is implemented by this library is compliant to the Dynamic Memory Structure defined in the NFC Forum document "Type 2 Tag Technical Specification Version 1.0 2017-08-28 [T2T]".

The Type 2 Tag memory has a size of 1024 bytes. It is organized in the following way:

Block Number	Byte0	Byte1	Byte2	Byte3	Type
0	Internal 0	Internal 1	Internal 2	Internal 3	Reserved
1	Internal 4	Internal 5	Internal 6	Internal 7	Reserved
2	Internal 8	Internal 9	Lock 0	Lock 1	Reserved
3	CC 0	CC 1	CC 2	CC 3	Reserved
4	Data 0	Data 1	Data 2	Data 3	Data
5	Data 4	Data 5	...	...	Data
...	...	...	...	...	Data
15	...	...	Data 46	Data 47	Data
16	Data 48	Data 49	...	...	Data
17	...	...	...	...	Data
...	...	...	...	...	Data
251	...	...	...	Data 991	Data
252	Lock	Lock	Lock	Lock	Lock
253	Lock	Lock	Lock	Lock	Lock
254	...	...	...	...	Lock
255	Lock	Lock	Lock	Rsvd	Lock

There are three block types:

Static reserved (16 bytes)
Data (992 bytes)
Dynamic Lock and Reserved bytes (16 bytes)

Static reserved

The static reserved bytes contain 10 internal bytes, 2 lock bytes, and 4 Capability Container bytes.

Internal bytes

The internal bytes depend on the UID length. They are set according to the following table:

Byte number	4-byte UID	7-byte UID	10-byte UID
Internal0	UID0	UID0	UID0
Internal1	UID1	UID1	UID1
Internal2	UID2	UID2	UID2
Internal3	UID3	BCC0 = CT ^ UID0 ^ UID1 ^ UID2	UID3
Internal4	BCC0 = UID0 ^ UID1 ^ UID2 ^ UID3	UID3	UID4
Internal5	0xFF	UID4	UID5
Internal6	0xFF	UID5	UID6
Internal7	0xFF	UID6	UID7
Internal8	0xFF	BCC1 = UID3 ^ UID4 ^ UID5 ^ UID6	UID8
Internal9	NFC Lib version	NFC Lib version	UID9

UID0 contains the manufacturer ID for Nordic Semiconductor and equals 0x5F.

CT stands for Cascade Tag byte and equals 0x88.

The UID bytes are stored in the nRF52 FICR registers (see the nRF52832 Product Specification and the nRF52840 Product Specification).

If you want to use UID bytes other than the ones from the FICR registers, use the nfc_t2t_parameter_set function with the NFC_T2T_PARAM_NFCID1 parameter. When choosing a custom UID, remember to follow the NFC Forum requirements.

Static Lock bytes

Both Static Lock bytes (Lock 0 and Lock 1) are set to 0xFF, which means that the CC area and the first 48 bytes of the data area of the tag can only be read, not written.

CC bytes

The Capability Container bytes (CC 0 - CC 3) are encoded as described in Section 4.6 of the Type 2 Tag Technical Specification. They cannot be used for storing application data. See the following table for the values of the CC bytes:

CC Byte Number	Meaning	Value
CC0	NFC magic number	0xE1
CC1	Document version number (v1.0)	0x10
CC2	Size of data area (992 bytes / 8)	0x7C
CC3	R/W access (read only)	0x0F

Data

Application data is organized in TLV blocks. The data area can contain one or more TVL blocks, up to a maximum data size of 992 bytes.

A TLV block contains the following fields:

T (required): block type
L (optional, depending on the T value): block length in number of bytes (field length if present: 1 or 3 bytes)
V (optional, depending on the T and L values): block value (present only if the L field is present and greater than 0), multibyte field with length equal to L field value

The following block types are defined:

TLV block name	Value of T field	Description
NULL TLV	0x00	Can be used for padding of memory areas. The NFC Forum Device shall ignore this.
Lock Control TLV	0x01	Defines details of the lock bits.
Memory Control TLV	0x02	Identifies reserved memory areas.
NDEF Message TLV	0x03	Contains an NDEF message.
Proprietary TLV	0xFD	Contains tag proprietary information.
Terminator TLV	0xFE	Contains the last TLV block in the data area.

To write data to the tag, use the Type 2 Tag library functions nfc_t2t_payload_set or nfc_t2t_payload_raw_set. nfc_t2t_payload_set configures a single NDEF TLV block based on a user-provided NDEF message. nfc_t2t_payload_raw_set does not configure a TLV block, but the provided data must be organized in a TLV structure.

Dynamic Lock and Reserved bytes

15 Dynamic Lock bytes are located after the data area. Each bit defines access conditions of 8 consecutive bytes of the tag data area, except for the first 48 bytes, whose access conditions are defined by Static Lock bytes. The Dynamic Lock bits are set to 1 to indicate that the tag is read-only.

The lock bytes are followed by 1 reserved byte (Rsvd) to get a multiple of 8 bytes.