STRFNFCA datasheet(35/74 Pages) STMICROELECTRONICS

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STRFNFCA

Commands

Doc ID 023077 Rev 10

35/74

5.9.3

Optimizing wake-up conditions

Using the Wake-up source register, it is possible to cumulate sources for a wake-up event. It

is strongly recommended to always set an external event as a possible wake-up source.

To cumulate wake-up sources, simply set the corresponding bits in the Wake-up source

low pulse on pin IRQ_IN (bit 3 set to ‘1’), set the register to 0x0A.

5.9.4

Using various techniques to return to Ready state

The Idle command and reply set offers several benefits to users by enabling various

methods to return the STRFNFCA to Ready state. Some methods are nearly automatic,

such as waiting for a timer overflow or a tag detection, but others consume more power

compared to the ones requesting a host action. A description of each method follows below.

Default setting: from POR to Ready state

After power-on, the STRFNFCA enters Power-up state.

To wake up the STRFNFCA and set it to Ready state, the user must send a low pulse on the

IRQ_IN pin. The STRFNFCA then automatically selects the external interface (SPI or

UART) and enters Ready state and is able to accept commSands after a delay of

approximately 6 ms (t3).

From Ready state to Hibernate state and back to Ready state

In Hibernate state, most resources are switched off to achieve an ultra-low power

consumption.

The only way the STRFNFCA can wake-up from Hibernate state is by an external event (low

pulse on pin IRQ_IN).

A basic Idle command is:

>>>0x07 0E 08 04 00 04 00 18 00 00 00 00 00 00 00 00

Note:

The Wake-up flag value is NOT significant when returning to Ready state from Hibernate

state or after a POR.

From Ready state to Sleep state and back to Ready state

Wake-up by external event (low pulse on IRQ_IN or SPI_SS pin)

In Sleep or Power-up states, operating resources are limited in function of the selected

wake-up source to achieve a moderate power consumption level.

An Idle command example when wake-up source is pin IRQ_IN:

>>>0x07 0E 08 01 00 38 00 18 00 00 60 00 00 00 00 00

A similar command can be implemented using pin SPI_SS as a wake-up source:

>>>0x07 0E 10 01 00 38 00 18 00 00 60 00 00 00 00 00

Wake-up by Timeout

The LFO is required to use the timer. However, this increases the typical power consumption

by 80 µA. Several parameters can be modified to reduce power consumption as much as

possible.

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