HT48R063/064/065/066/0662/067
grammed with the right data to ensure its correct opera-
tion, a process that is normally carried out during
program initialisation.
counting. A timer overflow condition and corresponding
internal interrupt is one of the wake-up sources, how-
ever, the internal interrupts can be disabled by ensuring
that the ETnI bits of the INTCn register are reset to zero.
To choose which of the three modes the timer is to oper-
ate in, either in the timer mode, the event counting mode
or the pulse width capture mode, bits 7 and 6 of the
Timer Control Register, which are known as the bit pair
TnM1/TnM0, must be set to the required logic levels.
The timer-on bit, which is bit 4 of the Timer Control Reg-
ister and known as TnON, provides the basic on/off con-
trol of the respective timer. Setting the bit high allows the
counter to run, clearing the bit stops the counter. Bits
0~2 of the Timer Control Register determine the division
ratio of the input clock prescaler. The prescaler bit set-
tings have no effect if an external clock source is used. If
the timer is in the event count or pulse width capture
mode, the active transition edge level type is selected by
the logic level of bit 3 of the Timer Control Register
which is known as TnEG. The TnS bit selects the inter-
nal clock source if used.
Event Counter 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.
Bit7 Bit6
Control Register Operating Mode
Select Bits for the Event Counter Mode
0
1
In this mode, the external timer TCn pin, is used as the
Timer/Event Counter clock source, however it is not di-
vided 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, TnE, 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 Coun-
ter will reload the value already loaded into the preload
register and continue counting. The interrupt can be dis-
abled by ensuring that the Timer/Event Counter Inter-
rupt Enable bit in the corresponding Interrupt Control
Register, is reset to zero.
Timer Mode
In this mode, the Timer/Event Counter can be utilised to
measure fixed time intervals, providing an internal inter-
rupt signal each time the Timer/Event Counter over-
flows. To operate in this mode, the Operating Mode
Select bit pair, TnM1/TnM0, in the Timer Control Regis-
ter must be set to the correct value as shown.
Bit7 Bit6
Control Register Operating Mode
Select Bits for the Timer Mode
1
0
In this mode the internal clock is used as the timer clock.
The timer input clock source is either fSYS , fSYS/4 or the
LXT oscillator. However, this timer clock source is fur-
ther divided by a prescaler, the value of which is deter-
mined by the bits TnPSC2~TnPSC0 in the Timer
Control Register. The timer-on bit, TnON must be set
high to enable the timer to run. Each time an internal
clock high to low transition occurs, the timer increments
by one; when the timer is full and overflows, an interrupt
signal is generated and the timer will reload the value al-
ready loaded into the preload register and continue
As the external timer pin is shared with an I/O pin, to en-
sure 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
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Timer Mode Timing Chart
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Event Counter Mode Timing Chart (TnEG=1)
Rev. 1.10
44
June 9, 2009
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
