XRA00 datasheet(34/40 Pages) STMICROELECTRONICS

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XRA00

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Using this information, the Reader may issue a

second PingID command to explore the popula-

tion of XRA00 devices in bin 3, reserving the

XRA00 devices detected in bin 5 for later analysis:

Query 2

[CMD] = 00001000b(PingID)

[PTR] = 00000000b(0)

[LEN] = 00000100b(4)

[VALUE] = 0111b(7)

This command explores 3 bits farther into the tree

towards the highest memory location from the

memory address containing the bits 0111b. In Fig-

ure 37., the bold borders show the branches that

contain the XRA00 devices. The two branches

shown in the second half of the drawing contain

groups of XRA00 devices that match Query 2.

These are the same XRA00 devices that respond-

ed to the first query in bin 3.

In this new query, the XRA00 modulation during

the reply interval will take place in bins 1 (response

0010111b), 6 (response 1100111b) and 7 (re-

sponse 1110111b) as shown in Figure 38. and in

bold in Figure 37. The Reader knows 7 address

bits of these XRA00 devices and at least 4 bits of

information concerning the other XRA00 branch

affected by Query 1 but reserved for later analysis.

Although it is not the fastest way to isolate and

identify XRA00 devices, the Reader may continue

with this method and use the PingID command to

follow a branch through the XRA00 ID space until

it has explored the entire XRA00 address and 16-

bit CRC of the XRA00 address.

The recommended way to perform an analysis of

a population of XRA00 devices is to take advan-

tage of the Reader's ability to detect contention in

the reply intervals. The "divide by eight" feature of

the PingID command makes it possible to very

quickly reduce the number of XRA00 devices re-

plying in each bin. Simulations with populations of

100 XRA00 devices show that with random ad-

dresses, an average of less than 4 PingID com-

mands are needed to isolate one XRA00 device. If

only one XRA00 replies in a given bin, the Reader

can decode the 8 bits of information sent from the

XRA00 and issue a ScrollID command to that

XRA00 using the [PTR] [LEN] and [VALUE] data

that successfully isolated the XRA00.

Figure 36. Reader Modulations and XRA00 Backscatter During PingID Reply for Query 1

101

110

ai10774

001

010

011

100

000

111

Reader

Bin

Modulation

Tag Backscatter

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