AS3956 datasheet(46/107 Pages) AMSCO

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[v1-11] 2018-Nov-14

AS3956 − Detailed Description

Extended Mode

Extended mode enables communication between the NFC

device and MCU by employing standard NFC Tag 2 Type READ

and WRITE commands for data transfer RF to MCU and Buffer

Load, Buffer Read, Clear Buffer and Transmit Buffer commands

for data transfer MCU to NFC device. The purpose of this

communication mode is to provide a simple data transfer

mechanism between a NFC device and a MCU while

guaranteeing correct timing and synchronization. This is

achieved by implementing a robust handshake mechanism.

This mode uses a part of the memory address space that is out

of range of the internal physical memory. The communication

between a NFC device and a MCU can be performed by using

WRITE/READ commands on address FCh – FFh. Block addresses

FCh to FFh, each block having 4 bytes, are mapped to the first

16 bytes of the internal Buffer. Writing to these addresses will

write to the Buffer and reading will read from Buffer. Data with

CRC or any other error will not be placed in the Buffer. Each

successful write operation on any of these blocks, AS3956 will

automatically reply with ACK. Maximum packet size for data

from NFC device to MCU is 16 bytes and for data from MCU to

NFC device is 12 bytes, as the last 4 bytes of the Read response,

which is 16 bytes, are reserved for flags.

Error handling in Extended mode is defined in Error Handling.

Data received from RF side are kept available until the MCU

reads the data. The implemented asynchronous transmission

protocol arbitrates on overlapping memory accesses

(producer-consumer principle) and complies with timing

constraints of both RF and SPI / I²C protocols regardless of the

MCU performance.

Extended mode can be configured by setting Configuration

Byte IC_CFG2 in EEPROM or the corresponding register ( IC

Configuration Register 2).

Extended mode uses an address space above the address space

of the internal EEPROM. It is then possible for a NFC device to

perform accesses to AS3956 internal memory and data transfer

to/from the MCU, without switching modes. This feature allows

the NFC device e.g. to request to the MCU a switch to Tunneling

mode with a simple WRITE command. The extended mode

communication employs a built-in buffer for communication.

Access to buffer from RF and SPI / I²C is mutually exclusive.

AS3956 ensures that buffer content shall be kept as long as the

AS3956 is powered (even in case RF field is not present) and as

long the tag is in SELECTED state. In case the RF field is switched

off and then on again, the buffer content will be reset.

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