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Revision 2.3

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AS3910

Data Sheet - A p p l i c a t i o n I n f o r m a t i o n

8.10.1 Set Default

This direct command puts the AS3910 in the same state as power-up initialization. All registers are initialized to the default state. Please note

that results of different calibration and adjust commands are also lost. This direct command is accepted in all operating modes.

8.10.2 Clear

This direct command stops all current activities (transmission or reception) and clears FIFO. It also clears Collision and Interrupt Registers. This

command has to be sent first in a sequence preparing a transmission (except in case of direct commands Transmit REQA and Transmit WUPA).

8.10.3 Transmit Commands

All Transmit commands (Transmit with CRC, Transmit without CRC, Transmit REQA and Transmit WUPA) are only accepted in case the

Transmitter is enabled (bit tx_en is set).

8.10.4 NFC Transmit Commands

The NFC transmit commands (NFC transmit with Initial RF Collision Avoidance, NFC transmit with Response RF Collision Avoidance, NFC

transmit with Response RF Collision Avoidance with n=0) are used to transmit requests and responses in the NFC mode. Before actual

transmission the RF Collision avoidance with Collision avoidance threshold defined in the NFCIP Field Detection Threshold Register is

performed.

In the command NFC transmit with Response RF Collision Avoidance n is randomly set in a range from 0 to 3, while in the command NFC

transmit with Response RF Collision Avoidance with n=0 it is set to 0. In case collision is detected during the RF Collision Avoidance the

transmission is not done and an interrupt is sent with flag INTR due to NFC event.

The NFC transmit commands switch on and off the transmission block, setting the Operation control bit tx_en in the NFC mode is not allowed.

Timing of the NFC transmit commands is according to the ISO/IEC 18092 standard. For some timings the ISO/IEC 18092 specifies a range.

Actual implementation in the AS3910 is the following:

An interrupt due to end of transmission is sent when RF field is switched off.

All NFC Transmit commands are only authorized in case the ISO mode configuration bit nfc is set and the oscillator and regulators are running.

010100

Squelch

Performs gain reduction based on the current noise level.

010101

Clear Squelch

Resumes gain settings which were in place before sending Squelch command

010110

Adjust regulators

Adjusts supply regulators according to the current supply voltage level

010111

Calibrate modulation depth

Starts sequence which activates the TX, measures the modulation depth and

adapts it to comply with the specified modulation depth

011000

Calibrate antenna

Starts the sequence to adjust parallel capacitances connected to TRIMx pins so

that the antenna LC is in resonance.

011001

Check antenna resonance

Measurement of antenna LC tank resonance to determine whether calibration is

needed.

011010

Clear RSSI

Clears RSSI bits and restarts the measurement

011100

Transparent mode

Enter in Transparent mode

Parameter

Symbol

Value

Unit

Note

Initial delay time

302

µs

Initial RF Collision Avoidance

RF waiting time

37.76

µs

Initial guard time

5.11

ms

Initial RF Collision Avoidance

Active delay time

151

µs

Response RF Collision Avoidance

Active guard time

84

µs

Response RF Collision Avoidance

Guard time after sending

response or request

65

µs

after sending a response or request. This time is not

specified in the ISO/IEC 18092.

Table 9. Direct Commands

Code

Command

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