ST25R3918 datasheet(59/142 Pages) STMICROELECTRONICS

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DS13490 Rev 1

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ST25R3918

Application information

141

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).

Duration time: 5 ms max.

This command is not accepted if external definition of the regulated voltage is selected in

the Regulator voltage control register (bit reg_s is set to 1).

4.4.11

Measure phase

This command measures the phase difference between the signals on the RFO outputs and

the signals on the RFI inputs and stores the result in the A/D converter output register.

This command enables the transmitter and phase detector, and performs an A/D conversion

of the output of the phase detector with the A/D converter in relative mode. The phase

measurement results can be calculated using the following formulas:



0 ≤ Φ ≤ 17º: result = 255



17 < Φ < 163º: angle [º] = 17 + (1 -result / 255) * 146



163 ≥ Φ ≥ 180º: result = 0

Duration time: 25 μs max.

4.4.12

Clear RSSI

The receiver automatically clears the RSSI bits in the RSSI display register and starts a new

measurement of the RSSI when a new reception is started (e.g. after a Transmit direct

command). Since the RSSI bits store the peak value (peak-hold type) eventual variation of

the receiver input signal will not be followed (this may happen in case of a long message or

test procedure).

The direct command Clear RSSI clears the RSSI bits in the RSSI display register, and

restarts the RSSI measurement. This allows to obtain multiple RSSI measurements during a

single reception.

4.4.13

Transparent mode

This command sets the receiver and transmitter into the transparent mode. The device

enters the transparent mode on the rising edge of the BSS signal of the SPI frame used to

send the direct command. The transparent mode is maintained as long as signal BSS is

kept high, that is, the following SPI command sent from the microcontroller will automatically

stop the transparent mode.

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