HT45R34 Holtek Semiconductor, HT45R34 Datasheet - Page 14

• Manufacturer Part Number: HT45R34
• Description: C/R to F Type 8-Bit OTP MCU
• Manufacturer: Holtek Semiconductor

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The TM0, TM1 bits define the operating mode. The event
count mode is used to count external events, which
means the clock source comes from an external TMR
pin. The timer mode functions as a normal timer with the
clock source coming from the f
measurement mode can be used to measure the high or
low level duration of an external signal on the TMR pin.
The counting is based on the f
event counting or timer mode, once the timer/event coun-
ter starts counting, it will count from the current contents
in the Timer/Event Counter to FFH. Once overflow oc-
curs, the counter is reloaded from the Timer/Event Coun-
ter preload register and an interrupt request flag TF; bit 5
of INTC0, is generated at the same time.
In the pulse width measurement mode, with the TON
and TE bits equal to one, once the TMR pin has re-
ceived a transient from low to high, or high to low if the
TE bit is 0, it will start counting until the TMR pin returns
to its original level and resets the TON bit. The mea-
sured result will remain in the Timer/Event Counter even
if the activated transient occurs again. Therefore, only a
single shot measurement can be made. The TON bit
must be set again by software for further measurements
to be made. Note that, in this operating mode, the
Timer/Event Counter starts counting not according to
the logic level but according to the transient edges. In
the case of a counter overflow, the counter is reloaded
from the Timer/Event Counter preload register and is-
sues an interrupt request just like the other two modes.
To enable a counting operation, the Timer ON bit, TON; bit
4 of TMRC, should be set to 1 . In the pulse width mea-
surement mode, the TON will be cleared automatically af-
ter the measurement cycle is completed. But in the other
two modes, the TON can only be reset by instructions. The
Timer/Event Counter overflow is one of the wake-up
sources. No matter what the operation mode is, writing a 0
to ETI can disable the interrupt service.
If the Timer/Event Counter is switched off, then writing
data to the Timer/Event Counter preload register will
also directly reload that data to the Timer/Event Coun-
ter. But if the Timer/Event Counter is already running,
data written to it will only be loaded into the Timer/Event
Counter preload register. The Timer/Event Counter will
Rev. 1.20
INT
INT
clock. The pulse width
clock source. In the
Timer/Event Counter
14
continue to operate until an overflow occurs. When the
Timer/Event Counter is read, the clock will be blocked to
avoid errors. As clock blocking may results in a counting
error, this must be taken into consideration by the pro-
grammer. Bit0~Bit2 of the TMRC register can be used to
define the pre-scaling stages of the internal clock source
of the Timer/Event Counter.
External RC Oscillation Converter
An external RC oscillation mode is implemented in the
device. The RC oscillation converter contains two 16-bit
programmable count-up counters.
The RC oscillation converter is comprised of the
TMRAL, TMRAH, TMRBL, TMRBH registers when the
RCO bit, bit 1 of RCOCR register, is 1 . The RC oscilla-
tion converter Timer B clock source may come from an
external RC oscillator. The Timer A clock source comes
from the system clock or from the system clock/4, deter-
mined by the RCOCCR register.
There are six registers related to the RC oscillation con-
verter, i.e., TMRAH, TMRAL, RCOCCR, TMRBH,
TMRBL and RCOCR. The internal timer clock is the in-
put to TMRAH and TMRAL, the external RC oscillation
is the input to TMRBH and TMRBL. The OVB bit, bit 0 of
the RCOCR register, decides whether Timer A over-
flows or Timer B overflows, then the RCOCF bit is set
and an external RC oscillation converter interrupt oc-
curs. When the RC oscillation converter mode Timer A
or Timer B overflows, the RCOCON bit is reset to 0
and stops counting. Writing to TMRAH/TMRBH places
the start value in Timer A/Timer B while reading
TMRAH/TMRBH obtains the contents of Timer A/Timer
B. Writing to TMRAL/TMRBL only writes the data into a
low byte buffer. However writing to TMRAH/TMRBH will
write the data and the contents of the low byte buffer into
the Timer A/Timer B (16-bit) simultaneously. Timer
A/Timer B is changed by writing to TMRAH/TMRBH but
writing to TMRAL/TMRBL will keep the Timer A/Timer B
unchanged.
R e a d i n g T M R A H / T M R B H w i l l a l s o l a t c h t h e
TMRAL/TMRBL into the low byte buffer to avoid false
timing problem. Reading TMRAL/TMRBL returns the
contents of the low byte buffer. Therefore, the low byte
October 15, 2007
HT45R34