ST25R3911B datasheet(32/116 Pages) STMICROELECTRONICS

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Mask receive data and Unmask receive data

After the direct command mask receive data the signal rx_on that enables the RSSI and AGC operation of the

receiver (see Section 1.1.2 Receiver) is forced to low, processing of the receiver output by the receive data

framing block is disabled. This command is useful to mask receiver and receive framing from processing the data

when there is actually no input and only a noise would be processed (for example in case where a transponder

processing time after receiving a command from the reader is long). Masking of receive is also possible using

Mask Receive timer. Actual masking is a logical or of the two mask receive processes.

The direct command unmask receive data is enabling normal processing of the received data (signal rx_on is set

high to enable the RSSI and AGC operation), the receive data framing block is enabled. A common use of this

command is to enable again the receiver operation after it was masked by the command mask receive data. In

case Mask Receive timer is running while command unmask receive data is received, reception is enabled, Mask

Receive timer is reset.

The commands mask receive data and unmask receive data are only accepted when the receiver is enabled (bit

rx_en is set).

Direct command chaining is possible.

IRQ due to termination of direct command is not produced.

Measure amplitude

This command measures the amplitude on the RFI inputs and stores the result in the A/D converter output

When this command is executed the transmitter and Amplitude Detector are enabled, the output of the Amplitude

Detector is multiplexed to the A/D converter input (the A/D converter is in absolute mode). The Amplitude

Detector conversion gain is 0.6 VINPP/ VOUT. One LSB of the A/D converter output represents 13.02 mVpp on the

RFI inputs. A 3 Vpp signal (the maximum allowed level on each of the two RFI inputs), results in 1.8 V output DC

voltage and will produce a value of 1110 0110b on the A/D converter output.

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.

ST25R3911B

Application information

DS11793 - Rev 6

page 32/116

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