ST25R3918 datasheet(58/142 Pages) STMICROELECTRONICS

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Application information

ST25R3918

58/142

DS13490 Rev 1

4.4.6

Mask receive data and Unmask receive data

The direct command Mask receive data disables processing of the receiver output by the

RX decoders, RSSI measurement, and AGC operation.

The direct command Unmask receive data enables processing of the received data by the

RX decoders, RSSI measurement and AGC operation. A common use of this command is

to re-enable the receiver operation after it was masked by the command Mask receive data.

If the Mask receive timer is still running while the direct command Unmask receive data is

received, reception is enabled, and the Mask receive timer is reset.

In passive target (card emulation) mode, the Unmask receive data command prepares the

RX decoders for a new data reception and clears the internal FDT timer. In passive target

mode, this direct command must be used only if no further transmission from the

ST25R3918 is planned and the device has to wait for the next command to be received.

4.4.7

Change AM modulation state

This command changes the AM modulation state from unmodulated to modulated, and vice

versa. This can be used to measure the AM modulation index with the direct command

Measure amplitude. The command only affects the regulator state and not the resistive

modulation state.

4.4.8

Measure amplitude

This command measures the amplitude of the RF signal on the RFI inputs and stores the

result in the A/D converter output register.

This command enables the transmitter and amplitude detector. The transmitter drives the

antenna, and the amplitude detector converts the differential RF signal received back

between RFI1 and RFI2 into a proportional DC voltage. This DC voltage is converted with

the A/D converter in absolute conversion mode into an 8-bit value and stored in the A/D

converter output register.

The amplitude detector conversion gain is 0.6 VinPP / Vout referenced to the RF signal on a

single RFI pin. Thus, one LSB of the A/D converter output represents 13.02 mVPP on either

of the RFI inputs.

Note:

The maximum allowed voltage level on an RFI pin is 3 VPP. This results in 1.8 V output DC

voltage of the amplitude detector and produces a value of E6h after A/D conversion.

Duration time: 25 μs max.

RF waiting time

TRFW

512

/ fc

n = 0…3 based on nfc_n<1:0> in Auxiliary

definition register

Active guard time

TARFG

75 µs +

NFC field on guard time

NFC Field ON guard time defined in the NFC

field on guard timer register.

NFCPIP-1 TARFG requirement:

> 75 µs + NFC field ON guard times (1024 / fc)

Table 12. Timing parameters of NFC field ON commands (continued)

Parameter

Symbol

Value

Unit

Notes

ST25R3918 Datasheet(PDF) 58 Page - STMicroelectronics

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