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M451
May. 4, 2018
Page
420
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1006
Rev.2.08
M4
51
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CNT = 0
Set
CMPDAT = 80
TIF = 1 and
Interrupt
Generation
Clear TIF as 0
and Set
CMPDAT = 200
CNT from 2
24
-1 to 0
CNT = 100
CNT = 200
CNT = 300
CNT = 400
CNT = 500
CNT = 2
24
-1
TIF = 1 and
Interrupt
Generation
Clear TIF as 0
and Set
CMPDAT = 500
TIF = 1 and
Interrupt
Generation
Clear TIF as 0
and Set
CMPDAT = 80
Figure 6.8-3 Continuous Counting Mode
Event Counting Mode
6.8.5.7
Timer controller also provides an application which can count the input event from Tx (x= 0~3) pin
and the number of event will reflect to CNT (TIMERx_CNT[23:0]) value. It is also called as event
counting function. In this function, EXTCNTEN (TIMERx_CTL[24]) should be set and the timer
peripheral clock source should be set as PCLKx (x= 0~1).
User can enable or disable Tx pin de-bounce circuit by setting CNTDBEN (TIMERx_EXTCTL[7]).
The input event frequency should be less than 1/3 PCLKx if Tx pin de-bounce disabled or less
than 1/8 PCLKx if Tx pin de-bounce enabled to assure the returned CNT value is correct, and
user can also select edge detection phase of Tx pin by setting CNTPHASE (TIMERx_EXTCTL[0])
bit.
In event counting mode, the timer counting operation mode can be selected as one-shot, periodic
and continuous counting mode to counts the counter value CNT (TIMERx_CNT[23:0]) for Tx pin.
External Capture Mode
6.8.5.8
The event capture function is used to load CNT (TIMERx_CNT[23:0]) value to CAPDAT
(TIMERx_CAP[23:0]) value while edge transition detected on Tx_EXT (x= 0~3) pin. In this mode,
CAPFUNCS (TIMERx_EXTCTL[4]) should be as 0 for select Tx_EXT transition is using to trigger
event capture function and the timer peripheral clock source should be set as PCLKx (x= 0~1).
User can enable or disable Tx_EXT pin de-bounce circuit by setting CAPDBEN
(TIMERx_EXTCTL[6]). The transition frequency of Tx_EXT pin should be less than 1/3 PCLKx if
Tx_EXT pin de-bounce disabled or less than 1/8 PCLKx if Tx_EXT pin de-bounce enabled to
assure the capture function can be work normally, and user can also select edge transition
detection of Tx_EXT pin by setting CAPEDGE (TIMERx_EXTCTL[2:1]).
In event capture mode, user does not consider what timer counting operation mode is selected,
the capture event occurred only if edge transition on Tx_EXT pin is detected.
Users must consider the Timer will keep register TIMERx_CAP unchanged and drop the new
capture value, if the CPU does not clear the CAPIF status.
Содержание ARM Cortex NuMicro M451 Series
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