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Demystifying the "Low Memory" of Aviation's Low-Memory Tags
Tego's CTO explains why most aviation applications will require at least 2 kilobits.
Jan 26, 2012—Tego's recently introduced TegoChip 2000, offering 2 kilobits of available memory, is an ideal RFID "Low Memory Tag" chip for applications in aviation (see Tego Offers New 2-Kilobit Chip). Outlined in the Air Transport Association (ATA) Spec 2000 standard, the Low Memory Tag format is intended to allow the widespread use of lower-cost tags that store an abbreviated version of a tag's birth record and a shorter form of its table of contents, as compared with the original aviation High Memory Tag format.
There has been some confusion, however, regarding the amount of memory actually required to support Low Memory Tag usage. There may be some instances in which 1-kilobit tags will suffice, but the reality is that slightly more memory is necessary, and aviation users will likely be disappointed by 1-kilobit tags as Low Memory Tag applications unfold. Here's why:
Although not mentioned in the released version of Spec 2000, aerospace companies are required to follow EPCglobal's Tag Data Standard when creating their Electronic Product Code (EPC) numbers (each tag's unique item identifier). Ratified in September 2011, version 1.6 of this standard specifies EPC numbers as large as 422 bits. Most companies are surprised to learn how large their EPC number is, and some find that it complicates the use of 1-kilobit tags.
2. Mandatory Birth-Record Fields
Because Spec 2000's abbreviated birth-record description can be difficult to follow, most companies look at the table of birth-record entries outlined there and assume they only need to include the three fields listed as "Mandatory": CAGE code, serial number and original part number. But the remaining fields are not optional—they are labeled as "Conditional," and Conditional fields are usually mandatory. For example, the "Date of Manufacture" field is mandatory for all new parts. These Conditional fields can use significant amounts of memory.
3. Shared Memory
The expectation is that the 1-kilobit RFID chips currently on the market have 1 kilobit of user memory available. However, that memory needs to be divided among the EPC Memory bank, the User Memory bank and other chip overhead, such as passwords and control. Because these divisions have definitive increments, a high percentage of this storage space becomes unusable; in fact, it is not uncommon to have less than 400 bits left over for user memory.
Users who have already encountered just one of these issues recognize an unwelcome surprise when it hits them. The repercussions of all three, taken together, are worse—here is a potent triad of snags that can render 1-kilobit low-memory tags too erratic for aviation use. Tags may work when used with items on a production line today, but next week could bring additional parts to be tagged with updated requirements, and the 1-kilobit memory is suddenly unable to support a Low Memory Tag application.
Tego has worked closely with the aerospace industry for many years in developing standards and improving the practical implementation of radio frequency identification on aviation parts. Users should be aware that there are underlying reasons why the TegoChip 2000 model was developed as a 2-kilobit solution for ATA Spec 2000 Low Memory Tag applications—it needed to cover all possible cases for Low Memory Tag requirements, and the smaller 1-kilobit memory option is simply unable to accomplish that goal.
Bob Hamlin is the chief technology officer at Tego, a provider of high-memory RFID chips and tags able to operate within harsh environments.
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