XRAG2

Reader-to-tag protocol

15/33

5.3

Reader-to-tag data encoding

A reader communicates with the tag using Pulse Interval Encoding (PIE), as specified in

EPCglobal class-1 generation-2 UHF RFID specification.

Figure 7.

PIE encoding

specified in the EPCglobal Class 1 generation 2 RFID UHF specification, revision 1.0.9.

5.4

Reader-to-tag communication start and calibration

As specified in the EPCglobal Class 1 generation 2 RFID UHF specification, revision 1.0.9,

a reader begins signaling to the tag with a preamble or frame-sync sequence.

A preamble sequence must precede a Query command to calibrate data rates during

communication from the reader to the tag and from the tag to the reader (see Figure 8). The

preamble denotes the start of an inventory round. The preamble is composed of the

delimiter, RTCal and TRCAL symbols:

●

RTcal corresponds to the duration of a ‘0’ and a ‘1’. When receiving the preamble, the

tag computes pivot = RTCAL/2 and decodes further coming data symbol shorter than

pivot as ‘0’, and data symbol longer than pivot as ‘1’.

●

TRcal in addition to the Divide ratio (DR) parameter transmitted in the Query command

is used by readers to specify the tag-to-reader backscatter link frequency

–

data rate for FM0 tag-to-reader base band modulation: LF=DR/TRcal

–

data rates for Miller tag-to-reader subcarrier modulation: LF/M (M specified during

Query command)

A frame-sync sequence must precede all other signaling (see Figure 9).

Table 6.

1.

Characterized only.

Parameter

Symbol

Min

Max

Units

RF pulse width

(2)

2.

max (2.265 Tari)

0.525 Tari

µs

3.

Tari is the reference time for reader-to-tag signaling, and is the duration of a ‘0’.

Tari

6.25

25

µs

tPW

tPW

Tari

0.5Tari

≤ x ≤ Tari

1.5Tari

≤ data-1 ≤ 2.0Tari

data-0

data-1

ai12311