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5.4
T
AG
Tag memory addressing begins at address zero (0x0000), with the highest
addressable memory location equal to one less than the total number of bytes in the
tag. Each address is equal to one byte (8-bits), where the byte is the smallest
addressable unit of data. So for example, writing 8-bytes to a tag beginning at
address 0 will fill addresses 0 to 7 with 64-bits of data in all.
Depending on the manufacturer, RFID labels, molded tags and embedded PCBs can
have differing memory storage capacities and organization. Tag memory is grouped
into blocks of bytes that can vary in organization from manufacturer to manufacturer.
Even when compliant to ISO standards, byte memory addressing can differ from one
manufacturer to another (for example, tag memory can be organized in blocks of 4 or
8 bytes, depending on the RFID IC). Additionally, a certain number of bytes may be
allocated for storage of security data. For more information regarding a specific RFID
tag's memory allocation, please refer to the IC manufacturer's published datasheets.
Escort Memory Systems has taken great care to simplify tag memory addressing.
The mapping from logical address to physical address is handled by the C0405-
Series Controller's operating system. Users only need to identify the starting address
location on the tag and the number of bytes to be read or written. However, extra
attention needs to be paid to the memory block structure when memory lock
commands are used. When data is locked, it cannot be altered. Caution should be
exercised when using memory lock commands as locked data cannot be unlocked,
even by Escort Memory Systems.
5 . 4 . 1
M a p p i n g T a g M e m o r y
Is it a Byte or a Bit?
Customers need to take into account that there are some RFID tag manufacturers
that measure and specify their tag memory sizes by the total number of bits, as this
method generates a much larger (8X) overall number designed to inflate their
specifications. Escort Memory Systems, on the other hand, prefers to specify total tag
memory sizes in terms of bytes (rather than in bits), as this method more closely
reflects how data is stored and retrieved from a tag and is typically what our
customers really want to know.
5 . 4 . 2
C r e a t i n g a n R F I D T a g M e m o r y M a p
Creating a tag memory map is much like creating a spreadsheet that outlines the
actual data you plan to capture as well as the specific tag memory locations in which
you wish to store said data. Tag memory maps should be carefully planned, simple
and straightforward. It is advisable to utilize more storage space than is initially
required, as inevitably a need will arise to hold more data.
C 0 4 0 5 - X X X - 0 1 O P E R A T O R ' S M A N U A L – R E V . 0 3
M
EMORY
C H A P T E R 5 : R F I D T A G S
P A G E 4 8 O F 7 5
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