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NXP Semiconductors
UM191812
PN544 C2 User Manual
191812
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© NXP B.V. 2010. All rights reserved.
User Manual
Rev. 1.2 — 2010-06-16
32 of 172
7.4.8.3 Duplex Communication
The PN544 is capable of receiving and sending data at the same time. This situation can
be recognized when the other channel is conveying a non zero value. As soon as a byte
is arriving which has a value greater than 0, it shall be handled as a regular frame and
shall therefore handle this byte as length information. The host shall then apply the clock
as long as there is data pending, whichever side has more data to convey.
B
LEN2
Duplex Communication
CRC
1
CRC
2
IRQ
MISO
SCK
H
B
LEN1
B
1
CRC
2
00
MOSI
NSS
Actual number of clocks
is max(LEN1, LEN2)
LEN
1
LEN
2
H
CRC
1
B
1
B
L2-1
If a transfer is finished in
one direction, it applies
zeros.
Fig 26. Sample SPI Duplex Transfer