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[v1-11] 2018-Nov-14

AS3956 − Application Information

The same NDEF Message TLV bytes can be obtained with a

single READ command, as the TLV occupies only 4 blocks and

the READ command returns 16 bytes. In case of longer NDEF

messages of course several READs are necessary until the

complete message has been read out.

Reading/Writing Through SPI / I²C

An MCU can write the NDEF Message TLV bytes [03 0C D1 01 08

55 01 61 6D 73 2E 63 6F 6D]hex into blocks 04h-07h by sending

the following 4 bytes sequences through SPI or I²C (as described

in the Wired Interfaces section of this datasheet):

Writing:

[40 08 03 0C D1 01]hex

[40 0A 08 55 01 61]hex

[40 0C 6D 73 2E 63]hex

[40 0E 6F 6D 00 00]hex

To read the same data bytes written in blocks 04h – 07h, the

MCU should send the bytes sequences below (2 clock cycles for

MODE and address and 4 additional clock cycles to read the

data sent from AS3956, refer to the Wired Interfaces section of

this datasheet):

[7F 08 00 00 00 00]hex

[7F 0A 00 00 00 00]hex

[7F 0C 00 00 00 00]hex

[7F 0E 00 00 00 00]hex

Using Extended Mode to Switch AS3956 into

Tunneling Mode

An NFC device can force the AS3956 in Tunneling mode by

sending a command via Extended to the MCU to switch the

AS3956 operating mode from Extended to Tunneling (refer to

Extended mode section of this datasheet for implementation

details). If the MCU should emulate a T4T after the switch,

AS3956 should be sent to SENSE state by the MCU with the

direct command “Go To Sense” (command code D1h) and the

NFC device should do a new anti-collision round for proper T4T

activation.

Using Tunneling Mode to Emulate a NFC Type 4

Tag

For T4T emulation the Tunneling mode has to be enabled by

setting the tun_mod bit of IC_CFG2 to 1 and the SELR to 0x20.

With this configuration, once AS3956 has passed anti-collision

and entered SELECTED state, all frames coming from the NFC

interface will be pushed to the BUFFER. That means also the

SENS_REQ, ALL_REQ, SSD_REQ, SEL_REQ and SLP_REQ will not

be executed by the AS3956, so MCU must send the tag to SLEEP

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