AN3433 datasheet(11/34 Pages) STMICROELECTRONICS

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AN3433

Management of CR95HF or STRFNFCA activity

Doc ID 019046 Rev 2

11/34

2.5

Optimizing wakeup conditions

Using the Wakeup source register, it is possible to cumulate sources for a wakeup event. It

is strongly recommended to always set an external event as a possible wakeup source.

To cumulate wakeup sources, simply set the corresponding bits in the wakeup source

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

2.5.1

Wakeup source register

Wakeup conditions are defined in the 8-bit wakeup condition register. These bits select one

or several external conditions to be evaluated by the device in order to exit Idle mode.

Bit 0: When set, the device will wake up and return to Ready state at the end of a predefined

cycle. The Time Out (TO) value is defined by the Max sleep and Wake Up period:

TO = (MaxSleep *(WuPeriod+1)*RT or RT= 256*tLFO = 8 ms

This bit must be set when using the timer as a possible wakeup source. It must be set during

Tag Detection Calibration to force a wakeup after the first Tag Detection trial.

Bit 1: When set, the device will wake up when a Tag is detected in the RF field. This bit must

also be set during Tag Detection Calibration or during Tag Detection (when the RF field is

active).

Bit 2: This bit is RFU.

Bit 3: When set, the device will wake up when an external interrupt (low level on pin IRQ_IN)

is detected. This is useful for SPI communications.

It is recommended to set this bit to ‘1’ in order to recover in the event of a system crash.

Bit 4: When set, the device will wake up when an external interrupt (low level on pin

|SPI_SS) is detected. This is useful for UART communication.

Bits [7:5] These bits are RFU.

Cumulation of wakeup conditions

The wakeup conditions selected in the Wakeup condition register can be cumulated.

When the device returns to Ready state, it is possible to use the RdReg command to read

the Wakeup condition register to know which event caused the device to wake up from Idle

mode.

Read Wakeup condition register:

08 03 62 01 00

Reply (‘xx’ represent the Wakeup condition register bits):

00 01 xx

This information is used after each iteration during the Tag Detection Calibration process to

determine the CalRef level. This level corresponds to the switching of the bits in the Wakeup

condition register from 0x02 (Tag Detector) to 0x01 (TimeOut) when using the device

previously calibrated in a free-air environment (no tags present).

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