PRELIMINARY

EMMICROELECTRONIC-MARINSA

P4022

5

Timing Characteristics

1)

All timings are derived from the on-chip oscillator, which can vary by 30%.

2)

The minimum low frequency GAP width for a single chip is 1 bit at its own clock frequency. The reader

must however allow for the 30% spread in clock frequencies possible in a group of tags. Therefore the

minimum width of the GAP in MUTE and WAKE-UP signals must be 1.5 bits. High frequency GAPs can

be arbitrarily narrow (specified as minimum 50 ns).

3)

The maximum GAP width for a single chip is 6 bits at its own clock frequency. The reader must

however allow for the 30% spread in clock frequencies possible in a group of tags. Therefore the

maximum width of the GAP in MUTE and WAKE-UP signals must be 5 bits.

Parameter

Symbol Test conditions

Min

Typ

Max Units

High frequency GAP width

50

ns

High frequency ACK GAP width

6

bit

High frequency MUTE and WAKE-UP GAP width

5

bit

Low frequency ACK GAP width

1.0

6

Bit

Low frequency MUTE and WAKE-UP GAP width

1.5

5

Bit

GAP separation in WAKE-UP signal

1.5

5

Bit

Table 6

Anti-collision Protocol Overview

The protocols are a collection of simple but fast

and reliable anti-collision protocols. They allow

fast reading of large numbers of transponders

simultaneously using a single reader. It is even

possible to identify transponders with identical

codes, thereby making it possible to count

identical items.

Free-running protocol

The basis of the BTG-Supertag series of protocols

is that transponders transmit their own codes at

random times to a reader. By just listening and

recording unique codes when they are received,

the reader can eventually detect every tag. The

reader detects collisions by typically checking a

CRC. This basic protocol is known as the “Free-

running” protocol. It requires uniquely coded tags.

Its main advantage is that the reader design is

simple, and the spectrum requirement is much

less – a very narrow band is required.

Bi-directional protocols

Allowing bi-directional communication between

reader and transponders can speed up the basic

free-running protocol. Communication from the

reader to transponders is achieved by turning the

illuminating energy field off for short periods. The

transponders detect these gaps in the energy

transmission and interpret them as required.

Switch-off and Slow-down Modes

Reducing the effective population of transmitting

transponders in the reader field can speed up the

free-running protocol.

One method to achieve

this is by either switching transponders off or

slowing them down once

they have been

detected. To achieve this, the reader sends an

ACK signal to a transponder after its code has

been successfully received. The transponder then

either switches off completely or reduces its

repeat rate until it is powered down. This reduces

the number of collisions between transponder

transmissions, thereby reducing the time required

to read a group of tags. The Switch-off protocol’s

main advantage is that identical transponders can

be counted.

In the P4022 the ACK signal is implemented as

two consecutive gaps with the appropriate timing

and received at a specific time after a code has

been transmitted.

Fast Mode

A second method of speeding up the reading of

tags, is to inhibit

other transponders from

transmitting while one transponder is transmitting.

This is done by sending a MUTE signal to all the

transponders when the start of a transmission is

detected.

The transponders stay muted long

enough to allow the transmission of one code.

This allows the transponder that has started

transmitting to complete its transmission without

any collisions. The other transponders continue