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MLX90111

128bit Read Write Transponder

Melexis Microelectronic Systems  

3 Timing specification

3.1 Asynchronous Control Pattern

The Asynchronous Control Pattern (ACP) is sent

by the reader to render the transponder silent

(stop transmitting), and listen for a programming

sequence.

Before starting the ACP, the field must be stable

at FHIGH for at least 5 bit periods (Tsetup). This

guarantees that the reference level

FTHRESHOLD is adjusted.

The control pattern itself contains 4 transitions

between high field FHIGH and low field FLOW,

each of which should be 2.5bitperiods apart.

The threshold level FTHRESHOLD adjusts itself

exponentially to the average FHIGH over the last

20 periods (TCLK).

The optimum modulation depth forced by the

reader depends on the application and stretches

between:

90%> (FHIGH-FLOW) / (FHIGH+FLOW) > 20%

The transponder samples the field 2 times per

bit. A first time is after the first quarter, the

second time after the third quarter. The sample

values are only retained when the modulation

resistor is off. The other samples are dropped.

3.2 Synchronous Command

When the ACP has been detected, the

transponder modulation will be turned off, within

maximum 6 bit periods after the last rising edge

of the ACP. The transponder will now

synchronize on the first falling edge it sees. This

edge is generated by a startbit (SB=0), which

has to be sent within a Timeout Window TWD.

If no SB is detected the transponder will return to

its original read mode.

The SB may used to optimize the

synchronization between tag and reader.

Tip: always try to put the sampling time of the

transponder at the end of the first half bit. This

minimizes the influence of an increased the

transponder Q at larger distance.

However, if the modulated signal on the

transponder takes several periods to drop, the

SB may be extended with this time. This will

shift the sampling moment forward.

After this synchronisation step, a synchronous

command can be sent from the base station.

Make sure to respect the nr of transponder

clocks per bit, as specified below.

All data sent by the reader have to be Return-

To-One encoded.

MLX90111

128bit Read Write Transponder

3.3 Transponder action

The command is verified on its Parity and CRC

values after the full command has been

received.

If verification is successful the command will be

executed during the next 32 bit periods.

Else if no valid command is received, due to a

verification error, the transponder will

immediately, i.e. 32 bit periods after the SB, start

modulating its 128bit ID code.

3.3 Multiple commands

After successfully receiving a command, the

transponder will wait for a new command. This

new timeout window (TWD) starts after the 32 bit

period it requires to execute the received

command.

To limit time skew between microcontroller and

the transponder, a new synchronization is done

before each new command.

The transponder will start modulating its ID code

approximately 52 btiperiods after successfully

having received its last command.

3.4 Other timings

See timing table below for an overview of all

timings. All timings are bitperiod based, and are

therefore related to the resonance frequency

and datarate.

MLX90111 128bit Read Write Transponder Page 8 of 12

Rev 1.12 5-Feb-01

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