XRA00SBN18I1GE STMicroelectronics, XRA00SBN18I1GE Datasheet - Page 33

• Manufacturer Part Number: XRA00SBN18I1GE
• Manufacturer: STMicroelectronics

Specifications of XRA00SBN18I1GE

• Lead Free Status / RoHS Status: Compliant

ANTI-COLLISION ALGORITHM
The PingID command divides a population of
XRA00 devices into eight sub-populations based
on their ID code by binning XRA00 responses into
eight separate time slices, or Bin Response Win-
dows. This binning provides the basis for an anti-
collision algorithm that probes the binary ID code
three bits at a time. Individual XRA00 devices can
be isolated from large populations in the field of
the Reader by issuing multiple PingID commands
to the field, analyzing the responses and eventual-
ly issuing the appropriate ScrollID command.
Figure 35.
first four LSBs in the XRA00 address space. Al-
though only the four first levels are shown, the bi-
nary tree structure applies to the entire XRA00 ID
code (96 bits for a Class-1b XRA00).
A PingID command with [PTR]=0, [LEN]=1 and
[VALUE]=0 will probe the right half of this tree (the
‘0’ branch) through the first four bits of the XRA00
memory.
Figure 35. First Four LSBs as a Binary Tree
Anti-Collision Example
Consider two XRA00 devices having their lowest
address programmed with 0111
spectively.
Query 1
[CMD] = 00001000
[PTR] = 00000000
[LEN] = 00000001
[VALUE] = 1
This command probes the left half of the tree
shown in
es the first bit of both XRA00 devices in the exam-
1111
111
Figure 35.
0111
is a binary tree representation of the
b
11
(1)
1011
011
b
b
b
(PingID)
(0x00)
(0x01)
The [VALUE] field of 1, match-
0011
1
1101
101
0101
b
and 1011
01
1001
001
0001
b
, re-
Similarly, a PingID command with [PTR]=0,
[LEN]=1 and [VALUE]=1 will probe the left half of
this tree (the ‘1’ branch) through the first four bits
of the XRA00 memory.
For the PingID command with [PTR]=0, [LEN]=1
and [VALUE]=0, XRA00 devices whose LSBs are
0000
LSBs are 0010
vices whose LSBs are 1110
Readers can look for backscatter modulation from
the XRA00 devices in each of the bins and learn
about the XRA00 population even if collisions
make reading the 8 bits of data sent by the XRA00
devices difficult.
The presence of backscatter in a given bin merely
indicates that one or more XRA00 device(s)
match(es) the query. The bin number tells the
Reader what the next three MSBs of the XRA00
addresses will be. The bin contents also indicate
the next 5 bits of the responding XRA00 devices.
ple (0111
respond.
During the reply interval, the XRA00 devices mod-
ulate the next 8 bits of their address data that
come just after the matched portion on the higher
address side. The bin in which they modulate is
determined by the three LSBs of the data they
modulate. At the Reader, backscatter modulation
is observed in bins 3 (011
shown in
es can modulate in each of these bins, contention
may be observed but the Reader knows that there
are two distinct populations of XRA00 devices
present whose first four LSBs are 0111
1011
1110
b
b
, respectively.
110
respond in bin 0, XRA00 devices whose
0110
Figure
b
10
and 1011
1010
b
respond in bin 1... and XRA00 de-
36.). Since multiple XRA00 devic-
010
0010
b
), so that they will both
0
1100
b
100
b
) and 5 (101
0100
respond in bin 7.
00
1000
000
0000
XRA00
b
b
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