ST95HF datasheet(40/93 Pages) STMICROELECTRONICS

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Commands

ST95HF

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DocID025630 Rev 4

Duration before Timeout = 256 * tL * (WU period + 2) * (MaxSleep + 1)

Note:

Note that: 0x00 < MaxSleep < 0x1F.

An Idle command example when wake-up source is timer (0x01) when fLFO = 32 kHz (mean

power consumption is 25 µA)

>>>0x07 0E 01 21 00 38 00 18 00 60 60 00 00 00 00 08

An Idle command example when wake-up source is timer (0xC1) when fLFO = 4 kHz (mean

power consumption is 20 µA):

>>>0x07 0E C1 21 00 38 00 18 00 60 60 00 00 00 00 08

The same command can be used mixing a timer and the IRQ_IN pin (0xC9) as a wake-up

source:

>>>0x07 0E C9 21 00 38 00 18 00 60 60 00 00 00 00 08

Wake-up by Tag Detection

In this mode, the typical consumption can greatly vary in function of parameter settings (WU

period without RF activity and Swing Count defining the RF burst duration). Using default

settings, consumption in the range of 100 µA can be achieved.

Tag Detector is a state where ST95HF is able to detect an RF event, a wake-up will occur

when a tag sufficiently modifies the antenna load and is detected by the ST95HF.

An Idle command example when wake-up source is Tag Detection (0x02):

>>>0x07 0E 02 21 00 79 01 18 00 20 60 60 64 74 3F 08

The same command can be used mixing Tag Detection and the IRQ_IN pin (0x0A) as a

wake-up source:

>>>0x07 0E 0A 21 00 79 01 18 00 20 60 60 64 74 3F 08

The tag detection sequence is defined by dedicated parameters:

•

WU source (Byte 3) (Wake-up source register on page 64)

–

The Timeout bit (bit 0) must be set to ‘1’ in order to manage a certain number of

emitted bursts. Otherwise, bursts will be sent indefinitely until a stop event occurs

(for example, tag detection or a low pulse on pin IRQ_IN).

–

The Tag Detect bit (bit 1) must be set to ‘1’ to enable RF burst emissions.

–

It is recommended to also set Bits 3 or 4 to ‘1’ to ensure that it is possible to leave

Tag Detect mode via an external event (for example, a low pulse on pin IRQ_IN).

•

WU period (Byte 10): Defines the period of inactivity (tINACTIVE) between two RF bursts:

tINACTIVE = (WuPeriod + 2) * tREF

•

OscStart, DacStart (Bytes 11 and 12): Define the set-up time of the HFO and Digital

Analog Converter, respectively. In general, 3 ms is used both set-up times.

HFO | DAC set-up time = (OscStart | DacStart) * tL

•

DacDataL, DacDataH (Bytes 13 and 14): Reference level for Tag Detection (calculated

during the tag detection calibration process).

•

SwingsCnt (Byte 15): Represents the number of 13.56-MHz swing allowed during a

Tag Detection burst. We recommend using 0x3F.

•

Maxsleep (Byte 16): The ST95HF emits (MaxSleep +1) bursts before leaving Tag

Detection mode if bit 0 (Timer Out) of the WU source register is set to ‘1’. Otherwise,

when this bit is set to ‘0’, a burst is emitted indefinitely.

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