CLRC632 Datasheet, PDF (88/163 Pages) NXP Semiconductors – Multiple Protocol Contactless Reader IC

Philips Semiconductors
Product Specification Rev. 3.0; May 2003
Multiple Protocol Contactless Reader IC
CL RC632
9.2.2 CONTROLLING THE TIMER UNIT
The main part of the timer unit is a down-counter. As long as the down-counter value is unequal zero, it
decrements its value with each timer clock.
If TAutoRestart is enabled the timer does not decrement down to zero. Having reached the value 1 the timer
reloads with the next clock with the TimerReload value.
The timer is started immediately by loading a value from the TimerReload Register into the counter module.
This may be triggered by one of the following events:
• Transmission of the first bit to the card (TxBegin Event) and bit TStartTxBegin is 1
• Transmission of the last bit to the card (TxEnd Event) and bit TStartTxEnd is 1
• Bit TStartNow is set to 1 (by the µ-Processor)
Note: Every start event reloads the timer from the TimerReload Register. Thus, the timer unit is re-triggered.
The timer can be configured to stop with one of the following events:
• Reception of the first valid bit from the card (RxBegin Event) and bit TStopRxBegin is set to 1
• Reception of the last bit from the card (RxEnd event) and bit TStopRxEnd is set to 1
• The counter module has decrement down to zero and bit TAutoRestart is set to 0
• Bit TStopNow is set to 1 (by the µ-Processor)
Loading a new value, e.g. zero, into the TimerReload Register does not immediately influence the counter,
since the TimerReload Register affects the counter units content only with the next start event. Thus, the
TimerReload Register may be changed even if the timer unit is already counting. The consequence of
changing the TimerReload Register will be visible after the next start event.
If the counter is stopped by setting bit TstopNow, no TimerIRq is signalled.
9.2.3 TIMER UNIT CLOCK AND PERIOD
The clock of the timer unit is derived from the 13.56 MHz chip clock via a programmable divider. The clock
selection is done with the TPreScaler Register that defines the timer unit clock frequency according to the
following formula:
1
2^{T Pr eScaler}
T_TimerClock = _fTimerClock = _13.56MHz
The possible values for the TPreScaler Register range from 0 up to 21 resulting in minimum time T_TimerClock of
about 74 ns up to about 150 ms.
The time period elapsed since the last start event is calculated with
T_Timer
=
TReLoadValue − TimerValue
f_TimerClock
resulting in a minimum time T_Timer of about 74 ns up to about 40 s.
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