R
EM4223
Transponders in the ROUND_STANDBY state will go
through an internal time-out sequence and will return to
the ROUND_ACTIVE state after a period equal to 2.5 X
176 tag bit periods has elapsed since the last MUTE
command if the WUS bit = 0 (this time-out may be over-
Each slot has a duration at least as long as the duration
of a Transponder preamble. The actual duration of the
slot is determined by the Transponder and is equal to 16
Transponder bit times. If a Transponder has selected the
current slot in which to transmit its reply, the Slot length
is increased for that Transponder to the duration of a
message length so that the Transponder can send its
complete message. In order to prevent other tags (those
that have not yet started their replies) from transmitting
during the first tag’s reply slot the Reader issues a MUTE
command to place the tags into the ROUND_STANDBY
state. After the active Transponder has finished
transmitting its message, and if the Reader has
successfully read the Transponder it issues a Next_Slot
command synchronously with the tag’s signature. If the
Transponder message was not successfully read then
the Reader issues a Close_Slot command, which will
cause all the tags currently in the ROUND_STANDBY
state to re-enter the ROUND_ACTIVE state.
ridden
by
the
Transponder
receiving
further
Standby_Round or MUTE commands from the Reader
which keep the Transponder in the ROUND_STANDBY
state).
The
Transponder
will
move
to
the
ROUND_ACTIVE state before the end of time-out period
if it receives a Next_Slot, Close_Slot, New_Round or
Wake_Up_FST command.
When the Transponder has reached the end of a round,
it will self-trigger a new round, randomly select a new slot
in which to transmit and it will transmit its identity or data
when it reaches the selected slot. The process continues
until the Transponder has been successfully read and
acknowledged by
a valid Next_Slot command or
removed from the RF energizing field.
The number of slots in a round, referred to as round size,
is determined by the Reader and is signaled to the
Transponder in the Wake_Up_FST or New_Round
command. In the FST mode the tag elects a default
roundsize of 16, which may be overridden by a Reader
command, however the FST mode is able to operate
without any round initializing command. During the
subsequent collision arbitration process the Reader
dynamically chooses an optimum round size for the
following rounds based on the number of collisions
and/or unproductive time in a round. The number of
collisions is a function of the number of Transponders in
the ROUND_ACTIVE state present in the Reader field
and the current round size. The Reader signals a change
in round size to Transponders by sending a New_Round
command containing the required round size.
If at any time the Transponder receives an Init_Round,
Init_Round_All or Begin_Round command whether in the
READY, ROUND_ACTIVE or ROUND_STANDBY
states, it will immediately switch to the ISO mode of
operation.
BOTH TYPES – READ ACKNOWLEDGE
When a Transponder which has transmitted its data in
the current slot, receives a Next_slot command, it:
Verifies that the signature in the command matches
the signature it sent in its last Reply
Verifies that the Next_Slot command has been
received within the timing window.
If the Transponder has met these acknowledge
conditions it enters the Quiet state. Otherwise, it remains
in the ROUND_ACTIVE state.
The Transponder on entering the ROUND_ACTIVE State
or on re-entering the ROUND_ACTIVE state having
completed a round, selects a pseudo slot at random in
which to reply. Pseudo slots are equal to Transponder
preamble in duration. If the Transponder has selected
the first pseudo slot, it will transmit immediately, if not it
will hold off until it has reached the selected pseudo-slot
and then transmit.
A Transponder in the Quiet state can only be returned to
the active population by means of a Reset_To_Ready
command followed by the appropriate round initializing
command or by removing it from the RF energizing field
for longer than the persistent sleep time.
On receiving and recognizing a valid Transponder
transmission preamble, the Reader sends a MUTE
command (SOF), which tells all Transponders that have
not yet started transmitting, to move to the
ROUND_STANDBY state. When the Reader receives
FST MODE OPTIONS
If the FST = 0 set and the WUS = 1, the Transponder will
wake up in Tag Talks First mode but muted. The first
Next_Slot command will move the Transponder to the
ROUND_ACTIVE state and it will enter a round as if it
had received a Wake_Up command.
the Transponder Reply without error, it sends
a
Next_Slot command containing the signature of the
Transponder that it has just received.
If both the WUS = 0 and FST = 0 the Transponder will
move directly to the ROUND_ACTIVE state as if it had
received a Wake_Up command.
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