mfrc531 NXP Semiconductors, mfrc531 Datasheet - Page 25

• Manufacturer Part Number: mfrc531
• Description: Iso/iec 14443 Reader Ic
• Manufacturer: NXP Semiconductors

NXP Semiconductors
MFRC531_34
Product data sheet
PUBLIC
9.5.2.1 Time-out and WatchDog counters
9.5.2.2 Stopwatch
9.5.2.3 Programmable one shot timer and periodic trigger
9.5.2 Using the timer unit functions
9.5.3 Timer unit registers
After starting the timer using TReloadValue[7:0], the timer unit decrements the TimerValue
register beginning with a given start event. If a given stop event occurs, such as a bit
being received from the card, the timer unit stops without generating an interrupt.
If a stop event does not occur, such as the card not answering within the expected time,
the timer unit decrements down to zero and generates a timer interrupt request. This
signals to the microprocessor the expected event has not occurred within the given time
(t
The time (t
the timer unit. Setting the TReloadValue register triggers the timer which in turn, starts to
decrement. If the defined stop event occurs, the timer stops. The time between start and
stop is calculated by the microprocessor using
decrement down to zero.
Programmable one shot timer: The microprocessor starts the timer unit and waits for
the timer interrupt. The interrupt occurs after the time specified by t
Periodic trigger: If the microprocessor sets the TAutoRestart bit, it generates an interrupt
request after every t
Table 22
Table 22.
Δt
Flags
TAutoRestart
TimerValue[7:0]
TReloadValue[7:0]
TPreScaler[4:0]
TRunning
TStartNow
TStartTxBegin
TStartTxEnd
TStopNow
TStopRxBegin
TStopRxEnd
Timer
=
).
(
TReLoad
shows the related flags of the timer unit in alphabetical order.
Timer
Associated timer unit registers and flags
) between a start and stop event is measured by the microprocessor using
value
Timer
–
Rev. 3.4 — 26 January 2010
TimerValue
cycle.
056634
Register name
TimerClock
TimerValue
TimerReload
SecondaryStatus
Control
TimerControl
TimerControl
Control
TimerControl
TimerControl
TimerClock
)
×
t
Timer
Equation
5, when the timer does not
Bit
5
7 to 0
7 to 0
4 to 0
7
1
0
1
2
2
3
ISO/IEC 14443 reader IC
Timer
MFRC531
© NXP B.V. 2010. All rights reserved.
.
Register address
0Ch
2Ch
05h
09h
2Bh
2Bh
09h
2Bh
2Bh
2Ah
2Ah
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