Product Specs

Table Of Contents
42 NFCT Near field communication tag
Page
422
Receive Transmit
Last data bit EoF
Logic ‘0’
Subcarrier continues in the 3 cases below
Logic ‘1’
Before Min
20/f
c
84/f
c
STARTTX task
FRAMEDELAYMAX
FRAMEDELAYMIN
SoF
Subcarrier modulation
Between Min and Max
STARTTX task
SoF
Subcarrier modulation
After Max (or missing)
STARTTX task
Subcarrier modulation
ERROR event
Figure 119: Frame timing controller (FRAMEDELAYMODE=Window)
42.6 Frame assembler
The NFC peripheral implements a frame assembler in hardware.
When the NFC peripheral is in the ACTIVE_A state, the software can decide to enter RX or TX mode. For
RX, see Frame disassembler on page 423. For TX, the software must indicate the address of the source
buffer in Data RAM and its size through programming the PACKETPTR and MAXCNT registers respectively,
then issuing a TXSTART task.
MAXCNT must be set so that it matches the size of the frame to be sent.
The STARTED event indicates that the PACKETPTR and MAXCNT registers have been captured by the
frame assembler's EasyDMA.
When asserting the STARTTX task, the frame assembler module will start reading
TXD.AMOUNT.TXDATABYTES bytes (plus one additional byte if TXD.AMOUNT.TXDATABITS > 0) from the
RAM position set by the PACKETPTR.
The NFC peripheral transmits the data as read from RAM, adding framing and the CRC calculated on the fly.
The NFC peripheral will take (8*TXD.AMOUNT.TXDATABYTES + TXD.AMOUNT.TXDATABITS) bits and
assemble a frame according to settings in TXD.FRAMECONFIG. Both short frames, standard frames and
bit oriented SDD frames as specified in the NFC Forum, NFC Digital Protocol Technical Specification can be
assembled by correct setting of the TXD.FRAMECONFIG register.
The bytes will be transmitted on air in the same order as they are read from RAM with a rising bit order
within each byte (least significant bit first). That is, b0 will be transmitted on air before b1, and so on. The
bits read from RAM will be coded into symbols as defined in the NFC Forum, NFC Digital Protocol Technical
Specification.
Important: Some NFC Forum documents, such as NFC Forum, NFC Digital Protocol Technical
Specification, define bit numbering in a byte from b1 (LSB) to b8 (MSB), while most other technical
documents from the NFC Forum, and also the Nordic Semiconductor documentation, traditionally
numbers them from b0 to b7. The present document uses the b0 to b7 numbering scheme. Be aware
of this when comparing with the NFC Forum, NFC Digital Protocol Technical Specification to others.
The frame assembler can be configured in TXD.FRAMECONFIG to add Start of Frame (SoF) symbol,
calculate and add parity bits, and calculate and add CRC to the data read from RAM when assembling
the frame. The total frame will then be longer than what is defined by TXD.AMOUNT.TXDATABYTES and
TXDATABITS. DISCARDMODE will select if the first bits in the first byte read from RAM or the last bits in the
last byte read from RAM will be discarded if TXD.AMOUNT.TXDATABITS are not equal to zero. Note that if
TXD.FRAMECONFIG.PARITY = Parity and TXD.FRAMECONFIG.DISCARDMODE=DiscardStart, a parity bit
will be included after the non-complete first byte. No parity will be added after a non-complete last byte.