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
63 of 172
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Fig 37. Clock request with HCI event
Step1:
As soon as the PN544 needs system clock, it sends the HCI event
NXP_EVT_CLK_REQUEST (with status byte set to ‘0x00’ for Clock request) to the Host
controller. Then system has to provide the clock. The acknowledgement from Host to
PN544 is detailed in the ‘clock acknowledge’ chapter.
Step2:
As soon as the PN544 does not need system clock, it sends the HCI event
NXP_EVT_CLK_REQUEST (with status byte set to ‘0x01’ for Clock release) to the Host
controller. Then system can disable the clock.
9.4.4 Clock Acknowledge
There are 3 ways to setup the clock acknowledgement.
9.4.4.1 Acknowledge with timeout
In this mode, PN544 will wait for a timeout to consider that system clock is available. The
timeout value is configurable from 0 to 255 ms (Recommended value is 10 ms or less).
To setup such a configuration, the following EEPROM area has to be set:
Table 55. Setting for clock acknowledge with timeout
Name
Length
(bytes)
Value(s)
Comments
PlClockAck
1
0x00
PN544 will wait for a
timeout to ensure that
system clock is available
PlClockTimeout
1
[0x00 to 0xFF]
Timeout value can be setup
with 1ms step, from 0 to
255 ms