1648
Binary data structures defined in the Tag Data Standard are intended for use in RFID 1649
Tags, particularly in UHF Class 1 Gen 2 Tags (also known as ISO 18000-6C Tags). The 1650
air interface standard [UHFC1G2] specifies the structure of memory on Gen 2 tags. 1651
Specifically, it specifies that memory in these tags consists of four separately addressable 1652
banks, numbered 00, 01, 10, and 11. It also specifies the intended use of each bank, and 1653
constraints upon the content of each bank dictated by the behavior of the air interface. 1654
For example, the layout and meaning of the Reserved bank (bank 00), which contains 1655
passwords that govern certain air interface commands, is fully specified in [UHFC1G2]. 1656
For those memory banks and memory locations that have no special meaning to the air 1657
interface (i.e., are “just data” as far as the air interface is concerned), the Tag Data 1658
Standard specifies the content and meaning of these memory locations. 1659
Following the convention established in [UHFC1G2], memory addresses are described 1660
using hexadecimal bit addresses, where each bank begins with bit 00h and extends
1661
upward to as many bits as each bank contains, the capacity of each bank being 1662
constrained in some respects by [UHFC1G2] but ultimately may vary with each tag make 1663
and model. Bit 00h is considered the most significant bit of each bank, and when binary
1664
fields are laid out into tag memory the most significant bit of any given field occupies the 1665
lowest-numbered bit address occupied by that field. When describing individual fields, 1666
however, the least significant bit is numbered zero. For example, the Access Password is 1667
a 32-bit unsigned integer consisting of bits b31b30…b0, where b31 is the most significant
1668
bit and b0 is the least significant bit. When the Access Password is stored at address 20h
1669
– 3Fh (inclusive) in the Reserved bank of a Gen 2 tag, the most significant bit b31 is stored
1670
at tag address 20h and the least significant bit b0 is stored at address 3Fh.
1671
The following diagram shows the layout of memory on a Gen 2 tag, The colors indicate 1672
the type of data following the categorization in Section Figure 1. 1673
1674
Figure 15. Gen 2 Tag Memory Map 1675
The following table describes the fields in the memory map above. 1676
Bank Bits Field Description Category Where
Specified Bank 00 (Reserved) 00h – 1Fh Kill Passwd
A 32-bit password that must be presented to the tag in order to complete the Gen 2 “kill” command. Control Info [UHFC1G2] 20h – 2Fh Access Passwd
A 32-bit password that must be presented to the tag in order to perform privileged operations
Control Info [UHFC1G2] Bank 01 (EPC) 00h – 0Fh
CRC A 16-bit Cyclic Redundancy Check computed over the contents of the EPC bank.
Control Info
[UHFC1G2]
Kill Passwd Access Passwd
Bank 00 (Reserved) Bank 01 (EPC) 00h 10h 20h 30h CRC PC Bits EPC 00h 10h 20h 40h 210h XPC Bits Bank 10 (TID) 00h 10h 20h 30h TID Bits Bank 11 (User) 00h 10h 20h 30h DFSID 08h
Encoded Data Elements
= Business Data = Control Information
= Tag Manufacture Information Filter value
Bank Bits Field Description Category Where Specified 10h –
1Fh
PC Bits Protocol Control bits (see below) Control Info (see below) 20h – end
EPC Electronic Product Code, plus filter value. The Electronic Product code is a globally unique identifier for the physical object to which the tag is affixed. The filter value provides a means to improve tag read efficiency by selecting a subset of tags of interest.
Business Data (except filter value, which is Control Info) The EPC is defined in Sections 6, 7, and 13. The filter values are defined in Section 10. 210h – 21Fh XPC Bits
Extended Protocol Control bits. If bit 16h of the EPC bank is set
to one, then bits 210h – 21Fh
(inclusive) contain additional protocol control bits as specified in [UHFC1G2] Control Info [UHFC1G2] Bank 10 (TID) 00h – end TID Bits
Tag Identification bits, which provide information about the tag itself, as opposed to the physical object to which the tag is affixed. Tag Manu- facture Info Section 16
Bank Bits Field Description Category Where Specified Bank 11 (User) 00h – end
DSFID Logically, the content of user memory is a set of name-value pairs, where the name part is an OID [ASN.1] and the value is a character string.
Physically, the first few bits are a Data Storage Format
Identifier as specified in [ISO15961] and [ISO15962]. The DSFID specifies the format for the remainder of the user memory bank. The DSFID is typically eight bits in length, but may be extended further as specified in
[ISO15961]. When the DSFID specifies Access Method 2, the format of the remainder of user memory is “packed objects” as specified in Section 17. This format is recommended for use in EPC applications. The physical encoding in the packed objects data format is as a sequence of “packed objects,” where each packed object includes one or more name-value pairs whose values are compacted together.
Business Data
[ISO15961], [ISO15962], Section 17
Table 4. Gen 2 Memory Map 1677
The following diagram illustrates in greater detail the first few bits of the EPC Bank 1678
(Bank 01), and in particular shows the various fields within the Protocol Control bits (bits 1679
10h – 1Fh, inclusive).
1681
Figure 16. Gen 2 Protocol Control (PC) Bits Memory Map 1682
The following table specifies the meaning of the PC bits: 1683
Bits Field Description Where
Specified 10h –
14h
Length Represents the number of 16-bit words comprising the PC field and the EPC field (below). See discussion in Section 15.1.1 for the encoding of this field.
[UHFC1G2]
15h User Memory
Indicator (UMI)
Indicates whether the user memory bank is present and contains data.
[UHFC1G2]
16h XPC Indicator
(XI)
Indicates whether an XPC is present [UHFC1G2]
17h Toggle If zero, indicates an EPCglobal application; in
particular, indicates that bits 18h – 1Fh contain
the Attribute Bits and the remainder of the EPC bank contains a binary encoded EPC. If one, indicates a non-EPCglobal application; in particular, indicates that bits 18h – 1Fh
contain the ISO Application Family Identifier (AFI) as defined in [ISO15961] and the remainder of the EPC bank contains a Unique Item Identifier (UII) appropriate for that AFI.
[UHFC1G2] 18h – 1Fh (if toggle = 0)
Attribute Bits Bits that may guide the handling of the physical object to which the tag is affixed.
Section 11
x00 xF x10 x14 x15 x16 x17 x18 x1F x20
CRC Length
User Memory Indicator (UMI) Toggle – always zero for EPC
EPC Binary Encoding Zero Fill to the word boundary Attribute /AFI PC NSI
Attribute bits for EPC
Bits Field Description Where Specified 18h – 1Fh (if toggle = 1)
AFI An Application Family Identifier that specifies a non-EPCglobal application for which the remainder of the EPC bank is encoded
[ISO15961]
Table 5. Gen 2 Protocol Control (PC) Bits Memory Map 1684
Bits 17h – 1Fh (inclusive) are collectively known as the Numbering System Identifier
1685
(NSI). It should be noted, however, that when the toggle bit (bit 17h) is zero, the
1686
numbering system is always the Electronic Product Code, and bits 18h – 1Fh contain the
1687
Attribute Bits whose purpose is completely unrelated to identifying the numbering 1688
system being used. 1689