AS3955 datasheet(46/111 Pages) AMSCO

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[v1-01] 2015-Apr-29

AS3955 − Detailed Description

Assuming that the internal buffer is empty, the NFC device may

start with data transmission by sending a WRITE command on

address FCh. When the first block is written, the rf_busy flag is

set and Rx start interrupt is triggered. At this point, the buffer

cannot be accessed over SPI / I²C until the entire write message

is received which is assumed to be complete when NFC device

sends a write command to block FFh. At this point, an Rx end

interrupt is triggered. This implies that a minimum two

messages must be received from a NFC device in order to

successfully complete a message. If a WRITE command is

received on address FFh before a WRITE command to address

FCh, AS3955 will assume that an error has occurred and will

respond as described in Error Handling.

When the reader writes into the last block FFh, rf_data_rdy flag

is set and the reader cannot change the buffer content until the

MCU reads the content of the block and clears the rf_data_rdy

flag. Any additional reception of WRITE commands from NFC

device, prior to MCU reading out the buffer content, shall result

in a response as defined in Error Handling. The blocks from

internal memory address space are directly mapped into buffer

space as shown on Figure 49.

Figure 49:

Mapping of Data Received into Buffer

When MCU reads out the data from the buffer, data will be sent

to MCU in the same order as they were stored in the buffer

starting from address 00h. When MCU has read all buffer

content, it shall issue a Clear Buffer command to clear the flag

rf_data_rdy. At this point, a new data message can be received.

00h

04h

08h

0Ch

00h

11h

22h

33h

44h

55h

66h

77h

88h

99h

AAh

BBh

CCh

DDh

EEh

FFh

Buffer address space

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

...

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