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AN3433

Example of CR95HF tag detection calibration process

Doc ID 019046 Rev 2

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Appendix C

Example of CR95HF tag detection calibration

process

From this Revision 1.1, we can directly use the CR95HF reply during Tag Detection

Calibration or Tag Detection sequences and avoid using the RDREG command.

This is a dichotomic approach to quickly converge to the DacDataRef value for which a

wakeup event switches from tag detection to timeout. In this process, only the DacDataH

parameter is changed in successive Idle commands. And we look at the wakeup event reply

to decide the next step.

<<< 00 01 02 corresponds to a Tag Detection (WakeUp_n = 2)

<<< 00 01 01 corresponds to a Timeout (WakeUp_n = 1)

REM, Tag Detection Calibration Test

REM,

Sequence: Power-up Tag Detect Wake-up by Tag Detect (1 try

measurement greater or equal to DacDataH) or Timeout

REM,

CMD 07 0E 03 A100 F801 1800 20 60 60 00 XX 3F 01

REM,

WU source = TagDet or Timeout

REM,

A100

Initial Dac Compare

REM,

F801

Initial Dac Compare

REM,

1800

HFO

REM,

20 WuPeriod = 32, Inactivity period = 256ms (LFO @ 32kHz)

REM,

60 Osc

3ms

(LFO @ 32kHz)

REM,

60 Dac

3ms

(LFO @ 32kHz)

REM,

DacDataL

= minimum level (floor)

REM,

DacDataH 00 = minimum level (ceiling)

REM,

Swing 13.56

4.6 us

REM,

01 Maximum number of Sleep before Wakeup 2

REM, Tag Detection Calibration Test

REM, During tag detection calibration process DacDataL = 0x00

REM, We execute several tag detection commands with different

DacDataH values to determine DacDataRef level corresponding to

CR95HF application set-up

REM, DacDataReg value corresponds to DacDataH value for which Wake-

up event switches from Timeout (0x01) to Tag Detect (0x02)

REM, Wake-up event

= Timeout

when

DacDataRef is between DacDataL

and DacDataH

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