ST25R3920B datasheet(63/158 Pages) STMICROELECTRONICS

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DS13890 Rev 4

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ST25R3920B

Application information

157

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 transmissions from the

ST25R3920B is planned and the devices have 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.

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.

4.4.9

Reset RX gain

This command initializes the AGC, Squelch and RSSI block and resets the gain reduction to

the value set in Receiver configuration register 4. Sending this command also stops any

ongoing squelch process.

4.4.10

Adjust regulators

When this command is sent, then the transmitter and receiver are enabled to ensure a high

current draw and the regulated voltage VDD_RF is set 250 mV below the power supply level

of VDD_TX. Before sending the adjust regulator command it is required to toggle the bit reg_s

by setting it first to 1 and then reset it to 0. After the adjustment is completed the state of the

transmitter and receiver prior to the command execution is restored (either enabled or

disabled).

ST25R3920B Datasheet(PDF) 63 Page - STMicroelectronics

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