UHF RFID tags knowledge

As UHF applications have been using more and more in our daily life , how to according to the practical application design system to achieve better use effect ? It is much useful to understand of the UHF tags related content. Today we can discuss about some of important knowledge of UHF memory.

 

EPC memory:

RFID tags goods coding region (EPC) by the CRC – 16, PC control (agreement), EPC of three parts.

RFID tags EPC item code area code parsing PC protocol control word.

 

PC protocol :

PC protocol control word contain physical layer information, the label tag in each inventory operations through its goods coding regions EPC returns the information. PC protocol control contains 16 bits in total, they are stored in the EPC store address h from 10 to 1 unit of fh, among them the meaning of each one are defined as follows:

10-14 h h: tag backscatter (PC + EPC) the length of all the word for:

000002: the length of the PC + EPC for a word (EPC length 0)

000012: PC + EPC for the length of the two words (EPC length for a word, 2 bytes, 16 bits)

000102: the length of the PC + EPC for three words (EPC length is 2 words, 4 bytes, 32 bits)

111112: the length of the PC + EPC of 32 words (EPC was 31 word length, 62 bytes, 496 bits)

15-17 h h: RFU (category 1 label for 0002).

18 h – 1 fh: the default value is 000000002, and can include such as ISO/IEC 15961 defines the AFI, counting system identification (NSI). NSI of MSB stored in 18 h storage location.

Our common RFID tag PC protocol control word is usually set to 3000 or 4000 h h:

PC protocol control word is set to 3000 h indicates EPC length is 6 words, 12 bytes, 96 bits.

PC protocol control word is set to 4000 h indicates EPC length of eight words, 16 bytes, 128 bits.

In the process of tag on electricity, the label should be controlled by PC protocol word in the first 5 bits specified PC + EPC length calculation it

CRC check code – 16, not through the EPC storage area length is calculated CRC – 16.

In EPC Class1 Gen2 (G2) protocol V109 version of the electronic label (Tag, label) and Reader (reading and writing), should have the following features.

Q1: the RFID tag memory is divided into several districts which?

A: the RFID Tag memory (Tag) is divided into Reserved memory (retention), EPC (electronic product code), TID (Tag identification number) and the User (User) four independent storage block (Bank).

Reserved area: store Kill Password (monkey) and Access Password (Access Password).

EPC area: store the EPC number, etc.

Every TID area: store tags identification number, number should be unique.

The User area: storing User defined data.

In addition to the Lock (Lock) status of each block and so on use and storage properties of units.

Q2: the tag which several states are there?

A: received continuous wave (the CW) irradiation on the electricity (Power – up), the label is Ready to be (prepare), Arbitrate (cutting), and the Reply (make) back, “Acknowledged (Reply), Open (Open), Secured (protection), Killed (inactivated) one of seven states.

1, the Ready state is not be inactivated after power on, start of the state, Ready to respond to commands.

2, in a state, Arbitrate mainly for waiting for the response to a Query command, etc.

After 3, response to a Query, enter a state of Reply, further response ACK command can send back the EPC number.

4, back to the EPC number, enter a state of “Acknowledged, can further response Req_RN command.

5, the Access Password not to 0 is allowed to enter the Open state, in this to read and write operations.

6, known only Access Password will enter a state of Secured, to read, write, lock, and so on.

7, into the Killed state label will remain unchanged, would never have to activate the radio frequency modulation signal, thus permanent failure. Be inactivated in all environments should be being Killed, into a state electricity is inactivated. Inactivated operation is irreversible.

To a tag into the state generally need to order a set of appropriate legal order, the command, in turn, also can only be effective when the label in the proper state, tag response after the command will turn to other condition.

Q3: command into which a few kinds?

A: from the point of view of command system architecture and expansibility, can be divided into Mandatory (essential), Optional (Optional), Proprietary (Proprietary) and Custom (Custom) four types.

Look from the use function, divided into label the Select (selected), the Inventory (stock) and three types of Access (Access) command.

In addition, in order to later command extension, reserved length different coding.

 

Q4: what are the essential (Mandatory) command?

A: in accordance with G2 protocol label and reading and writing, should support the essential command has 11: Select (choice), Query (Query), QueryAdjust (adjust the Query), QueryRep (repeated), ACK reply (EPC), NAK (to the cutting), Req_RN (random number request), Read (Read), Write (Write), the Kill (inactivated), the Lock (Lock).

Q5: what are Optional (Optional) command?

A: conform to the G2 protocol label and reading and writing, or might not support optional support command has three: Access (Access), BlockWrite (write), BlockErase (block erasure).

Q6: what is Proprietary (Proprietary) command will?

A: proprietary commands are used for manufacturing purposes, such as internal test label, the label factory after this command should be permanent failure.

Q7: Custom (Custom) command will have?

A: manufacturers can be defined and open to the user command, such as Philips company offer: BlockLock (lock), ChangeEAS state changes (EAS), EASAlarm alarm (EAS) command (EAS is commodity Electronic anti theft system Electronic Article Surveillance).

Q8: what are the selection (Select) command?

A: only A: Select, is essential.

Tag has multiple attributes, based on the user to set standards and policies, use the Select command, change some attributes and logo human choice or selects the label of a specific group of, can only count on them to identify or access operation, it is beneficial to reduce conflict and repeated recognition, speed up the recognition.

Q9: what are the Inventory (Inventory) command?

A: there are five: Query, QueryAdjust, QueryRep, ACK, NAK, is essential.

1, labels, after receiving the effective Query command, accord with the standard set of selected each TAB to create a random number (similar to roll the dice), and the random number to zero each label, will produce the echoes (back to the temporary password RN16 — a 16 – bit random number), and transferred to Reply status; If it meets the requirements of other labels will change some attributes and logo, so as to exit the tag clouds, is helpful to reduce duplication of recognition.

2, labels, after receiving the effective QueryAdjust orders, only labels for every new generate a random number (like heavy dice), the other with the Query.

3, labels, after receiving the effective QueryRep command, only to the label of each label in the original random number minus one, the other with the Query.

4, only simplification labels to receive an ACK effective command (using the above RN16, or Handle Handle, a temporary representative labels as to the identity of the 16 – bit random number. This is a security mechanism! After receive, send back the contents of the EPC area?? The most basic function of the EPC agreement.

5, labels, after receiving the valid NAK command, except in the Ready and Killed to keep the original state, the other is to Arbitrate.

Q10: what are the Access (Access) command?

A: there are five essential: Req_RN, Read, Write, Kill, Lock, and three optional, Access, BlockWrite, BlockErase.

1, labels, received effective Req_RN (with RN16 or Handle) after the command, back to the Handle, or a new RN16, depending on the state.

2, labels, received effective Read (with Handle) after the command, back to the type of error code, or the contents of the required block and Handle.

3, labels, received effective Write (with RN16 & Handle) after the command, back to the type of error code, or Write Handle success is sent back.

4, labels, received effective Kill (with the Kill Password, RN16 & Handle) after the command, back to the type of error code, Handle or inactivated success is sent back.

5, labels, received effective Lock (with Handle) after the command, back to the type of error code, or Lock Handle success is sent back.

6, labels, received effective Access (with the Access Password, RN16 & Handle) after the command, back to the Handle.

7, labels, received effective BlockWrite (with Handle) after the command, back to the type of error code, Handle or piece of writing success is sent back.

8, labels, received effective Block E

Q10: what are the Access (Access) command?

A: there are five essential: Req_RN, Read, Write, Kill, Lock, and three optional, Access, BlockWrite, BlockErase.

1, labels, received effective Req_RN (with RN16 or Handle) after the command, back to the Handle, or a new RN16, depending on the state.

2, labels, received effective Read (with Handle) after the command, back to the type of error code, or the contents of the required block and Handle.

3, labels, received effective Write (with RN16 & Handle) after the command, back to the type of error code, or Write Handle success is sent back.

4, labels, received effective Kill (with the Kill Password, RN16 & Handle) after the command, back to the type of error code, Handle or inactivated success is sent back.

5, labels, received effective Lock (with Handle) after the command, back to the type of error code, or Lock Handle success is sent back.

6, labels, received effective Access (with the Access Password, RN16 & Handle) after the command, back to the Handle.

7, labels, received effective BlockWrite (with Handle) after the command, back to the type of error code, Handle or piece of writing success is sent back.

8, labels, received effective BlockErase (with Handle) after the command, back to the type of error code, or block erasure Handle success is sent back.

Q11: so-called conflict (collisions) is how to return a responsibility, how to fight conflict? G2 what mechanism against conflict?

A: by the Q9 solutions mentioned above, when there is more than A random number with zero label back to different RN16, they are on the receiving antenna will appear different RN16 waveform superposition, also known as conflict (collisions), and so cannot be correctly decoded. Conflict has a variety of resistance mechanism can avoid the deformation of the wave superposition, for example, try to (time) to make a certain moment only a label “speaking”, then, the simplified processing can identify, speaking, reading and writing more than one label in each label.

“Command for the above three Q embodies the conflict resistance mechanism of G2: random number zero label to send back RN16, if there are multiple tags at the same time random number is zero, and can’t decode correctly, is strategically retransmission” Q “command or combination, for the selected tag clouds, until can decode correctly.

Q12: the tag identification number (dar) should have uniqueness? How to achieve?

A: the Tag identification number dar (the Tag identifier) is A sign of identity difference between tags (number) by analogy to the money. Think in terms of safety and security, any two G2 label should not be the same, the tag should have uniqueness; We know from the answer of Q1, label the four storage blocks

Q13: provide G2 the inactivated (Kill) command effect of the agreement? Whether to use the inactivated tag?

A: G2 agreement sets the Kill command, and use the password to control of 32 – bit, effective use Kill command tags will never produce modulation signal to activate after radiofrequency fields, thus permanent failure. But the original data may also in the label, not impossible to read them, can consider to improve the Kill command – with the meaning of erasing the data. It happens, people should be able to completely relieved.

In addition to a certain period of time, because of the G2 label use costs or other reasons, will be given to two or morethings tags can recycling reusable situation (such as User to use trays, boxes, with labels content change after the corresponding EPC number, User content to rewrite; Replace or pack labels to expensive and inconvenient. , etc.), need even be permanently lock the label content can also be rewritten command, because of the influence of different locked, only use the Write or BlockWrite, BlockErase command, not necessarily can rewrite the EPC number and User content or Password (such as label the EPC number is locked and cannot be changed, or is locked but forget the label Access Password and can’t go to rewrite the EPC number). The result is a demand, need a straightforward Erase command – in addition to dar area and the state of the Lock bits (dar after label can not be overridden), other EPC number, Reserved area, the contents of the User area and other state of the Lock, even the permanent Lock, will all be erasure for rewriting.

Compared to improve the Kill command and the increasing number of Erase command function is basically the same (including should use the Kill Password), the difference is that the former only Kill command that does not produce modulation signal, it also can be unified by Kill command to take different values of parameters RFU consideration.

Q14 during April 12-15: G2 Access (Access), and other command is optional, if labels or read/write device doesn’t support optional command?

A: if we do not support BlockWrite or BlockErase command, can completely by the Write command (A Write 16 – bit) using A few times more, because erasing can be thought of as 0, piece of writing, erasing the blocks of the former is several times of 16 – bit, other similar conditions of use.

If we do not support the Access command, only the Access Password is 0, into a state can only be Secured and can use the Lock command. In the Open or Secured state can change the Access Password, and then use the Lock command to Lock or permanent Lock Access Password (PWD – read/write bit is 1, permalock bits to 0 or 1, refer to the attached list), the label can not Secure

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