XRA00 datasheet(19/40 Pages) STMICROELECTRONICS

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XRA00

COMMAND-REPLY

System communications follow a two-phase com-

mand-reply pattern where the Reader initiates the

transaction (Reader Talks First, RTF). In the first

phase, the Reader provides power to one or more

passive XRA00 device(s) with continuous wave

RF energy. The XRA00 device(s) power(s) up in

the "Awake" state, where it is/they are ready to

process commands. The Reader transmits ampli-

tude-modulated information to the field using the

Reader-to-XRA00 encoding scheme described in

the Input Data Transfer from the Reader to the

XRA00 (Request Frame) paragraph. On comple-

tion of the transmission, the Reader ceases the

modulation and continues to apply the RF energy

to power the XRA00 device(s) during the reply

phase. The XRA00 device(s) communicate(s) with

the Reader via backscatter modulation during this

period, with the bit encoding scheme described in

the Answer Frame from the XRA00 to the Reader

paragraph.

Basic commands are designed to limit the amount

of state information the XRA00 device(s) have/has

to store between transactions. XRA00 devices on

the margin of the RF field are powered unreliably

and therefore cannot maintain a library of previous

transactions with the Reader. Consequently, the

basic command format centers on the notion of us-

ing "atomic" transactions with the XRA00 field.

This means that enough information is encased in

each command for XRA00 devices to respond ap-

propriately without having to refer to previous

transactions.

XRA00 State Diagram

In the state diagram shown in Figure 26., the Pow-

er Up state is entered from any other state when

power is first applied, or when power is no longer

sufficient for the XRA00 to operate normally as de-

scribed in Figure 10.

Power Up State. The XRA00 enters the power

up state on application of power, or when power

falls below the level required to operate the XRA00

internal logic. When power becomes acceptable

for operation, the XRA00 moves to the Awake

state.

Awake State. In the Awake state, the XRA00 in-

terprets commands. It reacts to the Reader Re-

quest Frame and parameters and switches to the

appropriate state. The Awake State is entered

from the Power Up State but can also be entered

from the Asleep State on receipt of a valid Talk

Command.

Reply State. The XRA00 switches to the Reply

state when, after receiving a valid Request Frame,

it has to generate a response. On completion of

the Answer Frame, the XRA00 returns to the

Awake State.

Asleep State. The XRA00 switches from the

Awake state to the Asleep state on receipt of the

Quiet Command. In the Asleep state, the XRA00

will only respond to the Talk command. Other

commands are ignored.

If power is removed from the XRA00, the device

enters the Persistence mode which allows it to

switch back to the Asleep state when the device is

powered up again.

Dead State. The XRA00 enters the Dead state on

receipt of a valid Kill command with the correct De-

struct Code sequence. In the Dead State the

XRA00 is Erased and does not provide valid ePC

data to the Reader.

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