AS3955 datasheet(45/111 Pages) AMSCO

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ams Datasheet

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[v1-01] 2015-Apr-29

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AS3955 − Detailed Description

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 AS3955 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. AS3955 ensures that buffer content shall be

kept as long as the AS3955 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.

NFC Device to MCU Data Flow Protocol

For the data transmission from NFC device to the MCU

employing the Extended mode, a NFC WRITE shall be used. Each

data transfer from NFC device is comprised of four WRITE

commands starting from address FCh and ending at address

FFh. The protocol implemented on a NFC device is expected to

always start the data transmission at address FCh, which signals

the beginning of the communication, and end at address FFh.

Figure 48 depicts regular implementation of the Extended

mode using the WRITE commands.

Figure 48:

Address Space Employed for Communication

FCh

FDh

FEh

FFh

00h

11h

22h

33h

44h

55h

66h

77h

88h

99h

AAh

BBh

CCh

DDh

EEh

FFh

Address space used for communication in

extended mode

...

WRITE FCh,00112233h

ACK, rf_busy = 1,

IRQ RX start = 1

WRITE FDh,44556677h

ACK, rf_data_rdy = 1,

IRQ RX end = 1

WRITE FEh,8899AABBh

WRITE hFF,CCDDEEFFh

ACK

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