ST25R95 datasheet(33/61 Pages) STMICROELECTRONICS

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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 varies widely 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 ST25R95 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 ST25R95.

An Idle command example when wake-up source is tag detection (0x02):

>>>0x07 0E 02 21 00 38 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 38 01 18 00 20 60 60 64 74 3F 08

The tag detection sequence is defined by dedicated parameters:

•

WU source (Byte 3), see Table 56. Wake-up source register

–

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 swings allowed during a tag detection burst. It is

recommend to use 0x3F.

•

Maxsleep (Byte 16): The ST25R95 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.

Note:

Use bytes 4 to 9 as shown in the examples in Section 5.9 Idle command (0x07) description.

The MaxSleep value is coded on the 5 least significant bits, hence 0x00 < MaxSleep < 0x1F.

All the previously described command parameters must be chosen accordingly for the initial tag detection

calibration when setting up the ST25R95.

Their value will impact tag detection efficiency, and ST25R95 power consumption during tag detection periods.

5.9.5

Tag detection calibration procedure

The Idle command allows the use of a tag detection as a wake-up event. Certain parameters of the Idle command

are dedicated to setting the conditions of a tag detection sequence.

During the tag detection sequence, the ST25R95 regularly emits RF bursts and measures the current in the

antenna driver IDRIVE using the internal 6-bit DAC.

When a tag enters the ST25R95 antenna RF operating volume, it modifies the antenna loading characteristics

and induces a change in IDRIVE, and consequently, the DAC data register reports a new value.

ST25R95

Idle command (0x07) description

DS12807 - Rev 4

page 33/61

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