Datasheet

PN512 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2016. All rights reserved.
Product data sheet
COMPANY PUBLIC
Rev. 5.2 — 16 June 2016
111352 96 of 137
NXP Semiconductors
PN512
Full NFC Forum-compliant frontend
14. Timer unit
A timer unit is implemented in the PN512. The external host controller may use this timer
to manage timing relevant tasks. The timer unit may be used in one of the following
configurations:
• Time-out counter
• Watch-dog counter
• Stop watch
• Programmable one-shot
• Periodical trigger
The timer unit can be used to measure the time interval between two events or to indicate
that a specific event occurred after a specific time. The timer can be triggered by events
which will be explained in the following, but the timer itself does not influence any internal
event (e.g. A time-out during data reception does not influence the reception process
automatically). Furthermore, several timer related bits are set and these bits can be used
to generate an interrupt.
Timer
The timer has an input clock of 13.56 MHz (derived from the 27.12 MHz quartz). The timer
consists of two stages: 1 prescaler and 1 counter.
The prescaler is a 12-bit counter. The reload value for TPrescaler can be defined between
0 and 4095 in register TModeReg and TPrescalerReg.
The reload value for the counter is defined by 16 bits in a range of 0 to 65535 in the
register TReloadReg.
The current value of the timer is indicated by the register TCounterValReg.
If the counter reaches 0 an interrupt will be generated automatically indicated by setting
the TimerIRq bit in the register CommonIRqReg. If enabled, this event can be indicated on
the IRQ line. The bit TimerIRq can be set and reset by the host controller. Depending on
the configuration the timer will stop at 0 or restart with the value from register
TReloadReg.
The status of the timer is indicated by bit TRunning in register Status1Reg.
The timer can be manually started by TStartNow in register ControlReg or manually
stopped by TStopNow in register ControlReg.
Furthermore the timer can be activated automatically by setting the bit TAuto in the
register TModeReg to fulfill dedicated protocol requirements automatically.
The time delay of a timer stage is the reload value +1.
The definition of total time is: t = ((TPrescaler*2+1)*TReload+1)/13.56MHz or if
TPrescaleEven bit is set: t = ((TPrescaler*2+2)*TReload+1)/13.56MHz
Maximum time: TPrescaler = 4095,TReloadVal = 65535
=> (2*4095 +2)*65536/13.56 MHz = 39.59 s
Example: