BS2824 Holtek Semiconductor Inc., BS2824 Datasheet - Page 55

• Manufacturer Part Number: BS2824
• Description: Touch Key Mcu
• Manufacturer: Holtek Semiconductor Inc.

Rev. 1.00
Event Counter Mode
Pulse Width Capture Mode
Control Register Operating Mode
Select Bits for the Event Counter Mode
Control Register Operating Mode
Select Bits for the Pulse Width Capture Mode
In this mode, a number of externally changing logic events, occurring on the external timer TCn pin,
can be recorded by the Timer/Event Counter. To operate in this mode, the Operating Mode Select bit
pair, TnM1/TnM0, in the Timer Control Register must be set to the correct value as shown.
In this mode, the external timer TCn pin, is used as the Timer/Event Counter clock source, however
it is not divided by the internal prescaler. After the other bits in the Timer Control Register have been
setup, the enable bit TnON, which is bit 4 of the Timer Control Register, can be set high to enable the
Timer/Event Counter to run. If the Active Edge Select bit, TnEG, which is bit 3 of the Timer Control
Register, is low, the Timer/Event Counter will increment each time the external timer pin receives a
low to high transition. If the TnEG is high, the counter will increment each time the external timer
pin receives a high to low transition. When it is full and overflows, an interrupt signal is generated
and the Timer/Event Counter will reload the value already loaded into the preload register and
continue counting. The interrupt can be disabled by ensuring that the Timer/Event Counter Interrupt
Enable bit in the corresponding Interrupt Control Register, is reset to zero.
As the external timer pin is shared with an I/O pin, to ensure that the pin is configured to operate as
an event counter input pin, two things have to happen. The first is to ensure that the Operating Mode
Select bits in the Timer Control Register place the Timer/Event Counter in the Event Counting
Mode, the second is to ensure that the port control register configures the pin as an input. It should be
noted that in the event counting mode, even if the microcontroller is in the Idle/Sleep Mode, the
Timer/Event Counter will continue to record externally changing logic events on the timer input
TCn pin. As a result when the timer overflows it will generate a timer interrupt and corresponding
wake-up source.
In this mode, the Timer/Event Counter can be utilised to measure the width of external pulses
applied to the external timer pin. To operate in this mode, the Operating Mode Select bit pair,
TnM1/TnM0, in the Timer Control Register must be set to the correct value as shown.
In this mode the internal clock, f
Timer/Event Counter. However, the clock source, f
prescaler, the value of which is determined by the Prescaler Rate Select bits T0PSC2~T0PSC0,
which are bits 2~0 in the Timer Control Register. After the other bits in the Timer Control Register
have been setup, the enable bit TnON, which is bit 4 of the Timer Control Register, can be set high to
enable the Timer/Event Counter, however it will not actually start counting until an active edge is
received on the external timer pin.
If the Active Edge Select bit TnEG, which is bit 3 of the Timer Control Register, is low, once a high
to low transition has been received on the external timer pin, the Timer/Event Counter will start
counting until the external timer pin returns to its original high level. At this point the enable bit will
be automatically reset to zero and the Timer/Event Counter will stop counting. If the Active Edge
Select bit is high, the Timer/Event Counter will begin counting once a low to high transition has
Event Counter Mode Timing Chart (TnEG=1)
SYS
, f
SYS
55
BS2824/BS2854/BS2868
/4 or the LXT, is used as the internal clock for the 8-bit
SYS
, for the 8-bit timer is further divided by a
Bit7
Bit7
0
1
Touch Key MCU
Bit6
Bit6
1
1
January 27, 2010