ST25R3910 datasheet(30/65 Pages) STMICROELECTRONICS

30 / 65 page

Functional overview

ST25R3910

30/65

DocID029768 Rev 2

NFCIP initiator

If the ST25R3910 is an NFCIP initiator, the microcontroller activates the oscillator and the

receiver, and prepares everything for transmitting as in case of the ISO-14443 transmission.

The transmission is actually executed by direct command NFC Transmit with Initial RF

Collision Avoidance.

The events that follow are the same as described in NFCIP target, with the difference that

the roles of the initiator and target are interchanged.

The Target Activation Detector may also be used in case of the NFCIP initiator operation to

detect the moment when the target RF field turns on and off.

1.2.14

AM modulation depth: definition and calibration

The AM modulation of the transmitted carrier is used for communication reader to tag in two

configuration cases:

•

ISO-14443B mode is configured in the ISO Mode Definition Register

•

Transparent mode with AM modulation (direct command Transparent Mode, bit am of

the Configuration Register 5 is set to 1)

In other cases the OOK modulation is used.

The AM modulation depth can be automatically adjusted by setting the Modulation Depth

Definition Register and sending the direct command Calibrate Modulation Depth. There is

also an alternative possibility where the command Calibrate Modulation Depth is not used

and the modulated level is defined by writing the Antenna Driver AM Modulated Level

Definition Register.

AM modulation depth definition using the direct command Calibrate

Modulation Depth

Before sending the direct command Calibrate Modulation Depth the Modulation Depth

Definition Register has to be configured in the following way:

•

Bit 7 (am_s) has to be set to 0 to choose definition by the command Calibrate

Modulation Depth

•

Bits 6 to 1 (mod5 to mod0) define target AM modulation depth

Definition of modulation depth using bits mod5 to mod0

The RFID standard documents usually define the AM modulation level in form of the

modulation index. The modulation index is defined as (a-b)/(a+b), where a and b are,

respectively, the amplitude of the non-modulated carrier and of the modulated carrier.

The bits mod5 to mod0 are used to calculate the amplitude of the modulated level. The non-

modulated level that was before measured by the A/D converter and stored in an 8 bit

binary decimals of this number.

Example

In case of the modulation index 10% the modulated level amplitude is 1.2222 times lower

than the non-modulated level.

1.2222 converted to binary and truncated to 6 decimals is 1.001110. So in order to define

the modulation index 10% the bits mod5 to mod0 have to be set to 001110.

ST25R3910 Datasheet(PDF) 30 Page - STMicroelectronics

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