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This value is then compared to the reference value established during the tag detection calibration process. This

enables the ST25R95 to decide if a tag has entered its operating volume.

The reference value (DacDataRef) is established during a tag detection calibration process using the ST25R95

application setting with no tag in its environment.

The calibration process consists in executing a tag detection sequence using a well-known configuration, with no

tag within the antenna RF operating volume, to determine a specific reference value (DacDataRef) that will be

reused by the host to define the tag detection parameters (DacDataL and DacDataH).

During the calibration process, DacDataL is forced to 0x00 and the software successively varies the DacDataH

value from its maximum value (0xFE) to it minimum value (0x00). At the end of the calibration process,

DacDataRef will correspond to the value of DacDataH for which the wake-up event switches from Timeout (no tag

in the RF field) to tag detected.

To avoid too much sensitivity of the tag detection process, it is recommended to use of a guard band. This value

corresponds to two DAC steps (0x08).

Recommended guard band value:

DacDataL = DacDataRef – Guard and DacDataH = DacDataRef + Guard

The parameters used to define the tag detection calibration sequence (clocking, set-up time, burst duration, etc.)

must be the same as those used for the future tag detection sequences.

When executing a tag detection sequence, the ST25R95 compares the DAC data register value to th DAC Data

parameter values (DacDataL and DacDataH) included in the Idle command. The ST25R95 will exit WFE mode

through a Tag detection event if the DAC data register value is greater than the DAC Data parameter high value

(DacDataH) or less than the DAC Data parameter low value (DacDataL). Otherwise, it will return to Ready state

after a Timeout.

An example of a basic Idle command used during the Tag detection Calibration process:

>>>0x07 0E 03 A1 00 F8 01 18 00 20 60 60 00 xx 3F 01

where xx is the DacDataH value.

5.10

Read Register (RdReg) command (0x08) description

This command is used to read the ACC_A, ARC_B, or Wakeup register.

Table 28. RdReg command description

Direction

Data

Comments

Example

Host to ST25R95

0x08

Command code

Ex 1. >>>

0x080369690100 (1)

Reads the ACC_A or ARC_B register.

Ex 2. >>>

0x0803620100

Reads the wakeup event register.

0x03

Length of data

0x62 or 0x69 Register address

0x01

0x00

ST Reserved

ST25R95 to Host

0x00

Result code

Ex 1. >>>

0x000113 (ARC_B register)

Depth = 1, Gain = 3. See Write

Ex 2. >>>

0x000101 Wakeup by timeout

Ex 3. >>>

0x000102 Wakeup by tag detect

<Len>

Length of data (= RegCount)

ST25R95 to Host

0x82

Error code

<<<0x8200 Invalid command length

0x00

Length of data

1. This command must be preceded by the setting of the ACC_A register index (

0x0903680004) or by setting the ARC_B

0x0903680001).

Note:

The Management of the analog register configuration register (ACC_A or ARC_B) is described in

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