AN3433 datasheet(26/34 Pages) STMICROELECTRONICS

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Tag Detection Calibration process

AN3433

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Doc ID 019046 Rev 2

Appendix B

Tag Detection Calibration process

The Tag Detection Calibration process must be performed when the application is initialized.

A fast and efficient dichotomist flow in 8 steps is proposed to achieve best results.

Before starting this flow, the user must define its basic setup which consists in defining the

following parameters using the Idle command. These parameters are described in

Section 2.3: Idle command parameters on page 9.

When using the CR95HF or STRFNFCA demoboard and development kit, the following

values are recommended:

●

Wakeup condition:

0x03 (tag detection or timeout)

●

EnterCtrlL/EnterCtrlH, WUCtrlL/WUCtrlH, and LeaveCtlL/LeaveCtrlH values define

internal parameters settings during the tag detection process. We recommend:

>>> 0xA1 00 F8 01 18 00

●

MaxSleep: MUST be set to ‘01’ in Tag Detection Calibration process for immediate

wakeup. This means that only one detection impulse will be sent and immediately

afterwards the device will exit Tag Detection Calibration mode.

●

Oscillator and DAC stabilization times. We recommend:

0x60

●

Number of 13.56 MHz swings during tag detection (SwingsCnt), we recommend using

0x3F to obtain a good reproducibility of measurements.

●

WakeUp period. This parameter is not used during the Tag Detection Calibration

process.

●

The Host can then use the RdReg command to read the Wakeup condition register to

determine the cause of the wakeup or check the reply code.

A basic Tag Detection Calibration command is:

>>> 0x 07 0E 03 A1 00 F8 01 18 00 20 60 60 00 xx 3F 01

B.1

Tag Detection Calibration algorithm

To determine the RF Field reference level (CalRef) corresponding to your application setup,

you must use the Tag Detection Calibration function (TagCal).

For calibration purposes, parameters are set to execute only one RF field evaluation before

leaving Tag Detection state.

This is achieved by setting the WU condition parameter to

0x03 (wakeup upon timeout or

tag detection) and the MaxSleep value to

0x01 forcing the CR95HF or STRFNFCA to leave

the Tag Detection state after only one attempt.

The value of the Wakeup flag is updated to the following value each time the device leaves

Tag Detection state.

Here, the

WakeUp_n variable corresponds to the third byte of the device Idle command

reply.

If the measured antenna current is between DacDataL and DacDataH, the wakeup

event will be a timeout:

WakeUp_n = 1

If the measured antenna current is less than DacDataL or greater than DacDataH, the

wakeup event will be a tag detection:

WakeUp_n = 2

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