ST95HF datasheet(39/93 Pages) STMICROELECTRONICS

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ST95HF

Commands

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 ST95HF 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 ST95HF enters Power-up state.

To wake up the ST95HF and set it to Ready state, the user must send a low pulse on the

IRQ_IN pin. The ST95HF then automatically selects the external interface (SPI) 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 ST95HF 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.

The Duration before Timeout is defined by parameters WU period and MaxSleep,

respectively 0x60 and 0x08 in the following example.

ST95HF Datasheet(PDF) 39 Page - STMicroelectronics

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