AN108711 - NXP Semiconductors

Philips Semiconductors
Figure 2 Reaching the NFC Protocol
Application Note
Tips and Tricks for PN51x Integration
Figure 2 shows that the Active Mode is the most straightforward (and fastest) way to
reach the NFC protocol. The protocol flow is described in a more detailed way in the next
chapter.
1.4.1 Passive Communication mode
In passive mode the Initiator first has to check if there is already an existing RF field. If
yes, it is not allowed to act as Initiator. If no RF field is detected, the Initiator starts the
communication by generating the RF field and sending the data according to the
appropriate bit representation at the selected bit rate. The target then answers to an
initiator command in a load modulation scheme, where the type of modulation also
depends on the bit rate. The Initiator always generates the RF field for the target. As long
as the RF field is on (and detected by the Target) the session context 5 is valid. If the RF
field has been switched off (or the Target lost the RF field), a new session (including the
initialization sequence) has to be started again.
5. The term “session context” is not specified in NFCIP-1, however, it will be used in this document to
specify the actions between the beginning and the end of a communication
© Koninklijke Philips Electronics N.V. 2006. All rights reserved.
Application note Rev. 01.10 — 11. May 2006 7 of 37