AN2319
Application note
Using the 64-bit UID in contactless RFID applications
Introduction
All STMicroelectronics contactless memory products provide a 64-bit unique identifier (UID)
for use with RFID applications. The 64-bit UID is a value written by STMicroelectronics
during the manufacturing process and it is guaranteed unique for each contactless memory.
This UID can be used by the final application system to identify each tag individually and
also, depending on the recognized memory type, to modify memory access models and
maps.
This application note describes how STMicroelectronics handles the 64-bit UID and how
applications can decode its value.
January 2009 Rev 2 1/8
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Contents AN2319
Contents
1 UID description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Unique serial number [41:0] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Product code [47:42] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Silicon manufacturer code [55:48] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4 Tag registration category [63:56] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Application examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 Example 1: high-level mnemonic source code . . . . . . . . . . . . . . . . . . . . . . 5
3.2 Example 2: low-level mnemonic source code . . . . . . . . . . . . . . . . . . . . . . 6
4 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
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AN2319 UID description
1 UID description
The 64-bit UID of STMicroelectronics provides a maximum of 242 (4,398,046,511,104)
unique ID tags per family.
Table 1. 64-bit unique identifier (UID) description
Bits [63:56] [55:48] [47:42] [41:0]
Size (bits) 88642
Val ue
Tag registration
category (0xD0)
Silicon manufacturer
code (0x02)
1.1 Unique serial number [41:0]
These 42 bits are the traceable unique serial number.
1.2 Product code [47:42]
These 6 bits store the STMicroelectronics product code. This code is unique for each tag
family product and that is why it can be used by the contactless system to identify the
product in the reader's antenna field. Once recognized, the contactless system knows the
command set and available memory map. Tab le 2 lists the product codes that identify
current products.
Table 2. ST product code chart
Binary Decimal SR product
00 0010 2 SR176
00 0011 3 SRIX4K
00 0100 4 SRIX512
00 0110 6 SRI512
Product code
Unique serial
number
00 0111 7 SRI4K
00 1100 12 SRT512
1.3 Silicon manufacturer code [55:48]
This bit field identifies the Silicon manufacturer code. Value 0x02 is dedicated for
STMicroelectronics in compliance with ISO 7816-6/AM1 specifications.
1.4 Tag registration category [63:56]
This bit field corresponds to the Registration category for RFID applications. Value 0xD0 is
attributed to ISO14443-B standard devices.
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Implementation AN2319
2 Implementation
The body of a loop (see Example 1) is used by a reader to detect and identify RFID tags.
This loop starts by switching the reader RF output OFF and then back ON again. This safely
resets any tags in the field and puts them in a READY state.
By issuing the INITIATE() command, the tag enters ACTIVE (SR176) or INVENTORY
(SRIxx) mode.
A non-zero response to the INITIATE() command indicates the presence of a tag and
enables the reader to obtain the ChipID.
This ChipID is used as a link to the tag for the following SELECT() command.
After a successful SELECT() command, the tag is ready for read / write operations.
Once the value of the UID is known, the application can easily determine and set the
important parameters for communication with the particular tag using the switch()
statement shown in Example 1: high-level mnemonic source code.
In certain applications and when using certain tags, it is necessary to identify the tag
product type. In this case, it is recommended to first read the tag UID value (which contains
the product type value) as shown in Example 2: low-level mnemonic source code.
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AN2319 Application examples
3 Application examples
Acquiring the UID is quite easy when using high-level SRIxx tags, but additional actions are
required when using low-level SR176 memories.
After sending the INITIATE() and SELECT() command sequence to the tag(s), send a
GET_UID() command to identify UID values.
SRIxx tags directly return the UID after receiving the GET_UID() command, while SR176
tags do not reply to this command.
If a tag is detected in the reader RF field but no reply is returned after a GET_UID()
command, it is probably a SR176 tag. In this case, the reader must read a specific memory
address to retrieve its UID as shown in Example 2.
The example shown in Section 3.2 is the body of the CRX14_Get_UID() function used in
Example 1.
3.1 Example 1: high-level mnemonic source code
This is an example of a UID acquisition loop using a high-level mnemonic source code.
UCHAR UID[8];
UCHAR blockSize, NoOfBlock, WriteblockAddress;
/********************************************
**** Manage all SRxx
********************************************/
CRX14_Set_Param(0x00); //RF Off (accessing the Parameter Register of CRX14)
CRX14_Set_Param(0x10); //RF On
if (CRX14_Initiate()) // (INITIATE() command)
{
CRX14_Select(Chip_ID); (SELECT() command)
CRX14_Get_UID(UID);
if((UID[7]==0xd0)&&(UID[6]==0x02))
switch (((UID[5] & 0xFC)>>2))
{
case 2: //SR176
blockSize=2; NoOfBlock=16; WriteblockAddress=4;
break;
case 3: //SRIX4K
blockSize=4; NoOfBlock=128; WriteblockAddress=7;
break;
}
}
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Application examples AN2319
3.2 Example 2: low-level mnemonic source code
This is an example of the body of a function used to acquire the UID using a low-level
mnemonic source code.
UCHAR buff[]; //actual copy of Input/Output Frame Register of CRX14
send_get_UID_Command(); (GET_UID() command)
if(buff[0]=0x0) //we may deal with SR176
{
read_a(0); //common read function (READ_BLOCK() command)
if(buff[0]!=0x0)
{
UID[0] = buff[1];
UID[1] = buff[2];
read_a(1);
UID[2] = buff[1];
UID[3] = buff[2];
read_a(2);
UID[4] = buff[1];
UID[5] = buff[2];
read_a(3);
UID[6] = buff[1];
UID[7] = buff[2];
}
}
The follow-up processing of the UID is the same for all product types as shown in
Example 1.
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AN2319 Revision history
4 Revision history
Table 3. Document revision history
Date Revision Changes
28-Feb-2006 1 Initial release.
20-Jan-2009 2 Table 2: ST product code chart updated.
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AN2319
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