ST25R3912 datasheet(45/130 Pages) STMICROELECTRONICS

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DS11794 Rev 9

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ST25R3912

Functional overview

Duration time: 25 μs max.

This command is accepted in case en (bit 7 of the Operation control register) is set and Xtal

oscillator frequency is stable.

Direct command chaining is not possible.

IRQ due to termination of direct command is produced after command execution is

terminated.

Squelch

This direct command is intended to avoid demodulation problems of transponders that

produce a lot of noise during data processing. It can also be used in a noisy environment.

The operation of this command is explained in Squelch.

Duration time: 500 μs max.

This command is only accepted when the transmitter and the receiver are operating.

Command is actually executed only in case signal rx_on is low.

Direct command chaining is not possible.

IRQ due to termination of direct command is not produced.

Reset Rx gain

This command initializes the AGC, Squelch and RSSI block. Sending this command stops a

squelch process in case it is going on, clears the current Squelch setting and loads the

manual gain reduction from Receiver configuration register 4.

This command is accepted in case en (bit 7 of the Operation control register) is set and Xtal

oscillator frequency is stable.

Direct command chaining is possible.

IRQ due to termination of direct command is not produced.

Adjust regulators

When this command is sent the power supply level of VDD is measured in maximum load

conditions and the regulated voltage reference is set 250 mV below this measured level to

ensure maximum possible stable regulated supply (see Section 1.2.10: Power supply

system). The use of this command increases the system PSSR.

At the beginning of execution of the command, both the receiver and transmitter are

switched on to have the maximum current consumption, and the regulators are set to their

maximum regulated voltage (5.1 V in case of 5 V supply and 3.4 V in case of 3.3 V supply).

After 300 μs VSP_RF is compared to VDD, if is not at least 250 mV lower the regulator setting

is reduced by one step (120 mV in case of 5 V supply and 100 mV in case of 3.3 V supply)

and measurement is done after another 300 μs. The procedure is repeated until VSP_RF

drops at least 250 mV below VDD, or until the minimum regulated voltage (3.9 V in case of

5 V supply and 2.4 V in case of 3.3 V supply) is reached.

Duration time: 5 ms max.

This command is accepted if en (bit 7 of the Operation control register) is set and Xtal

oscillator frequency is stable.

This command is not accepted when the external definition of the regulated voltage is

selected in the Regulator voltage control register(bit reg_s is set to H).

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