AS3955 datasheet(48/111 Pages) AMSCO

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[v1-01] 2015-Apr-29

AS3955 − Detailed Description

Figure 51:

Data Transmission from MCU to NFC Device

When the NFC device has successfully read all data from the

buffer, it shall clear the buffer and prepare for further data

transfer by issuing a WRITE command to address FFh. This will

trigger a Tx end interrupt.

If a READ command is received on address FCh prior to the

Transmit Buffer command, AS3955 will return zero data, io_busy

set to 1 and io_data_rdy set to 0. A NFC device can then poll

AS3955 by continuously sending READ commands at address

FCh and waiting until the last word equals 01h.

A READ command can be issued only to address FCh. Issuing a

READ command to any other address than FCh while in

Extended mode shall be treated as an error.

In Extended mode, it is assumed that AS3955 will always receive

16 bytes and transmit 12 bytes of data, 3 empty bytes and 1

byte for FLAGS. If the message size differs in any direction, then

the MCU or NFC device are responsible for proper error

management.

FCh

FDh

FEh

FFh

00h

11h

22h

33h

44h

55h

66h

77h

88h

99h

AAh

BBh

00h

FLAGS

Address space used for communication in

extended mode

...

READ FCh

io_busy = 1, io_data_rdy = 0

Response : 00000000h,

00000000h,

00000002h

READ FCh

io_busy= 0, io_data_rdy = 1

Response : 00112233h,

44556677h,

8899AABBh,

00000001h

WRITE FFh,

00000000h

io_busy = 0, io_data_rdy = 0

Response : ACK

io_busy

io_data_rdy

FLAGS:

b7 b6 b5 b4

rf_busy

rf_data_rdy

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