ST25R3918 datasheet(57/142 Pages) STMICROELECTRONICS

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DS13490 Rev 1

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ST25R3918

Application information

141

If no external field is detected, then the ST25R3918 transmitter is switched on automatically

(bit tx_en in the Operation control register is set) and an I_apon IRQ is signaled. After the

RF guard time defined in the NFC field on guard timer register has passed an I_cat IRQ is

signaled. At this point the controller can initiate a data transmission using a transmit

command.

If an external field is detected a I_cac IRQ is signaled, and the ST25R3918 transmitter stays

off.

The direct command NFC initial field ON performs an Initial collision avoidance according to

NFCIP-1 standard, and the direct command NFC response field ON performs a Response

collision avoidance according to NFCIP-1 standard. See Figure 25, Figure 26 and Table 12

for details on the timing of these commands.

Figure 25. Direct command NFC initial field ON

Figure 26. Direct command NFC response field ON

MS42450V1

TIDT

TIRFG

n x TRFW

Start

RF on

TRFW

MS42451V1

TADT

TARFG

n x TRFW

Start

RF on

TRFW

Table 12. Timing parameters of NFC field ON commands

Parameter

Symbol

Value

Unit

Notes

Initial delay time

TIDT

4096

/ fc

NFC initial field ON

RF waiting time

TRFW

512

/ fc

n = 0…3 based on nfc_n<1:0>

Initial guard time

TIRFG

75 µs +

NFC field on guard time

NFC field on guard time defined in the NFC field

on guard timer register.

NFCIP-1 TIRFG requirement: 5 …35 ms

Active delay time

TADT

768

/ fc

NFC response field ON

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