HT46R01/HT46R02/HT46R03
Configuring the Event Counter Mode
At this point the T0ON or T1ON bit, depending upon
which counter is used, will be automatically reset to zero
and the timer will stop counting. If the T0E or T1E bit is
high, the timer will begin counting once a low to high
transition has been received on the external timer pin
and stop counting when the external timer pin returns to
its original low level. As before, the T0ON or T1ON bit
will be automatically reset to zero and the timer will stop
counting. It is important to note that in the Pulse Width
Measurement Mode, the T0ON or T1ON bit is automati-
cally reset to zero when the external control signal on
the external timer pin returns to its original level,
whereas in the other two modes the T0ON or T1ON bit
can only be reset to zero under program control. The re-
sidual value in the timer, which can now be read by the
program, therefore represents the length of the pulse re-
ceived on the external timer pin. As the T0ON or T1ON
bit has now been reset, any further transitions on the ex-
ternal timer pin, will be ignored. Not until the T0ON or
T1ON bit is again set high by the program can the timer
begin further pulse width measurements. In this way,
single shot pulse measurements can be easily made. It
should be noted that in this mode the counter is con-
trolled by logical transitions on the external timer pin and
not by the logic level. As in the case of the other two
modes, when the counter is full, the timer will overflow
and generate an internal interrupt signal. The counter
will also be reset to the value already loaded into the
preload register. If the external timer pin is pin-shared
with other I/O pins, to ensure that the pin is configured to
operate as a pulse width measuring input pin, two things
have to happen. The first is to ensure that the
T0M1/T0M0 or T1M1/T1M0 bits place the Timer/Event
Counter in the pulse width measuring mode, the second
is to ensure that the port control register configures the
pin as an input. It should be noted that a timer overflow
and corresponding timer interrupt is one of the wake-up
sources. Note that the timer interrupts can be disabled
by ensuring that the ET0I or ET1I bits in the INTC0 reg-
ister are reset to zero.
In this mode, a number of externally changing logic
events, occurring on the external timer pin, can be re-
corded by the internal timer. For the timer to operate in
the event counting mode, the bit pair, T0M1/T0M0 or
T1M1/T1M0, depending upon which timer is used, must
be set to 0 and 1 respectively. The timer-on bit T0ON or
T1ON, depending upon which timer is used, must be set
high to enable the timer to count. Depending upon which
counter is used, if T0E or T1E is low, the counter will in-
crement each time the external timer pin receives a low
to high transition. If T0E or T1E is high, the counter will
increment each time the external timer pin receives a
high to low transition. As in the case of the other two
modes, when the counter is full, the timer will overflow
and generate an internal interrupt signal. The counter
will then preload the value already loaded into the
preload register. As the external timer pins are
pin-shared with other I/O pins, 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
T0M1/T0M0 or T1M1/T1M0 bits place the Timer/Event
Counter in the event counting mode, the second is to en-
sure that the port control register configures the pin as
an input. It should be noted that a timer overflow is one
of the interrupt and wake-up sources. Note that the timer
interrupts can be disabled by ensuring that the ET0I or
ET1I bits in the INTC0 register are reset to zero.
Configuring the Pulse Width Measurement Mode
In this mode, the width of external pulses applied to the
external timer pin can be measured. In the Pulse Width
Measurement Mode the timer clock source is supplied
by the internal clock. For the timer to operate in this
mode, the bit pair, T0M1/T0M0 or T1M1/T1M0, depend-
ing upon which timer is used, must both be set high. De-
pending upon which counter is used, if the T0E or T1E
bit is low, once a high to low transition has been received
on the external timer pin, the timer will start counting un-
til the external timer pin returns to its original high level.
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Event Counter Mode Timing Chart
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Pulse Width Measure Mode Timing Chart
Rev. 1.00
21
September 21, 2007
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
