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Table Of Contents

42 NFCT — Near field communication tag

Page

423

The Frame Assemble operation is illustrated in Figure 120: Frame assemble on page 423 for different

settings in TXD.FRAMECONFIG. All shaded bits fields are added by the frame assembler. Some of these

bits are optional and appearances are configured in TXD.FRAMECONFIG. Please note that the frames

illustrated do not necessarily comply with the NFC specification. The figure is only to illustrate the behavior of

the NFC peripheral.

Data from RAM

Byte 1: PACKETPTR + 0 Byte 2: PACKETPTR + 1

Byte (TXDATABYTES) Byte (TXDATABYTES + 1)

Frame on air

PARITY = Parity, TXDATABITS = 0, CRCM ODETX = CRC16TX

Byte 1 Byte 2

Byte (TXDATABYTES)

(only if TXDATABITS > 0)

C b

PARITY = Parity, TXDATABITS = 4, CRCMODETX = NoCRCTX, DISCARDMODE = DiscardStart

Byte 1 Byte 2 Byte (TXDATABYTES) Byte (TXDATABYTES + 1)

SoF

EoF

PARITY = Parity, TXDATABITS = 0, CRCMODETX = NoCRCTX

Byte 1 Byte TXDATABYTES

SoF

EoF

Figure 120: Frame assemble

The accurate timing for transmitting the frame on air is set using the frame timing controller settings.

42.7 Frame disassembler

The NFC peripheral implements a frame disassembler in hardware.

When the NFC peripheral is in the ACTIVE_A state, the software can decide to enter RX or TX mode. For

TX, see Frame assembler on page 422. For RX, the software must indicate the address of the destination

buffer in Data RAM and its size through programming the PACKETPTR and MAXCNT registers respectively,

then issuing a ENABLERXDATA task.

The STARTED event indicates that the PACKETPTR and MAXCNT registers have been captured by the

frame disassembler's EasyDMA.

When an incoming frame starts, the RXFRAMESTART event will get issued and data will be written to the

buffer in Data RAM. The frame disassembler will verify and remove on the fly any parity bits and SoF and

End of Frame (EoF) symbols based on RXD.FRAMECONFIG register configuration. It will, however, verify

and transfer the CRC bytes into RAM, if the CRC is was enabled through RXD.FRAMECONFIG.

When an EoF symbol is detected, the NFC peripheral will assert the RXFRAMEEND event and write the

RXD.AMOUNT register to indicate numbers of received bytes and bits in the data packet. The module does

not interpret the content of the data received from the remote NFC device, except for SoF, EoF, parity and

CRC checking, as described above. The Frame disassemble operation is illustrated in Figure 121: Frame

disassemble illustration on page 423.

Per NFC specification, the time between end of frame to the next start of frame can be as short as 86 µs,

so care must be taken that PACKETPTR and MAXCNT are ready and ENABLERXDATA is issued on time

after the end of previous frame. The use of a PPI shortcut from TXFRAMEEND to ENABLERXDATA is

recommended.

Frame on air

PARITY = Parity, RXDATABITS = 0, CRCMODERX = CRC16RX, RXDATABITS = 0

Byte 1

Byte 2 Byte RXDATABYTES

C b

PARITY = Parity, CRCMODERX = NoCRCRX, RXDATABITS = 4

Byte 1 Byte 2 Byte RXDATABYTES Byte (RXDATABYTES+1)

SoF

EoF

PARITY = NoParity, CRCMODERX = NoCRCRX, RXDATABITS = 0

Byte 1 Byte 2

Byte RXDATABYTES

SoF

EoF

Data to RAM

Byte 1: (PACKETPTR + 0) Byte 2: (PACKETPTR + 1) Byte RXDATABYTES Byte (RXDATABYTES+1)

Figure 121: Frame disassemble illustration

(only if RXDATABITS > 0)

SoF

CRC

1 (8 b

it)

2 (8

it)

EoF

SoF

CRC

1 (8 b

it)

2 (8

it)

EoF