Product data

MFRC631 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
Product data sheet
COMPANY PUBLIC
Rev. 3.3 — 4 February 2014
227433 9 of 120
NXP Semiconductors
MFRC631
High performance ISO/IEC 14443 A/B reader solution
8.2 Timer module
Timer module overview
The MFRC631 implements five timers. Four timers -Timer0 to Timer3 - have an input
clock that can be configured by register T(x)Control to be 13.56 MHz, 212 kHz, (derived
from the 27.12 MHz quartz) or to be the underflow event of the fifth Timer (Timer4). Each
timer implements a counter register which is 16 bit wide. A reload value for the counter is
defined in a range of 0000h to FFFFh in the registers TxReloadHi and TxReloadLo. The
fifth timer Timer4 is intended to be used as a wakeup timer and is connected to the
internal LFO (Low Frequency Oscillator) as input clock source.
The TControl register allows the global start and stop of each of the four timers Timer0 to
Timer3. Additionally, this register indicates if one of the timers is running or stopped. Each
of the five timers implements an individual configuration register set defining timer reload
value (e.g. T0ReloadHi,T0ReloadLo), the timer value (e.g. T0CounterValHi,
T0CounterValLo) and the conditions which define start, stop and clockfrequency (e.g.
T0Control).
The external host may use these timers 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 timer
• Periodical trigger
The timer unit can be used to measure the time interval between two events or to indicate
that a specific event has occurred after an elapsed time. The timer register content is
modified by the timer unit, which can be used to generate an interrupt to allow an host to
react on this event.
The counter value of the timer is available in the registers T(x)CounterValHi,
T(x)CounterValLo. The content of these registers is decremented at each timer clock.
If the counter value has reached a value of 0000h and the interrupts are enabled for this
specific timer, an interrupt will be generated as soon as the next clock is received.
If enabled, the timer event can be indicated on the pin IRQ (interrupt request). The bit
Timer(x)Irq can be set and reset by the host controller. Depending on the configuration,
the timer will stop counting at 0000h or restart with the value loaded from registers
T(x)ReloadHi, T(x)ReloadLo.
The counting of the timer is indicated by bit TControl.T(x)Running.
The timer can be started by setting bits TControl.T(x)Running and
TControl.T(x)StartStopNow or stopped by setting the bits TControl.T(x)StartStopNow and
clearing TControl.T(x)Running.
Another possibility to start the timer is to set the bit T(x)Mode.T(x)Start, this can be useful
if dedicated protocol requirements need to be fulfilled.