HT48R0662G View Datasheet(PDF) - Holtek Semiconductor
Part Name
Description
MFG CO.
'HT48R0662G' PDF : 126 Pages View PDF
HT48R064G/065G/066G/0662G
Enhanced I/O Type 8-Bit OTP MCU with OPA
Timer/Event Counters
The provision of timers form an important part of any microcontroller, giving the designer a means of
carrying out time related functions. The devices contain from one to three count-up timer of 8-bit
capacity. As the timers have three different operating modes, they can be configured to operate as a
general timer, an external event counter or as a pulse width capture device. The provision of an internal
prescaler to the clock circuitry on gives added range to the timers.
There are two types of registers related to the Timer/Event Counters. The first is the register that
contains the actual value of the timer and into which an initial value can be preloaded. Reading from
this register retrieves the contents of the Timer/Event Counter. The second type of associated register
is the Timer Control Register which defines the timer options and determines how the timer is to be
used. The device can have the timer clock configured to come from the internal clock source. In
addition, the timer clock source can also be configured to come from an external timer pin.
Configuring the Timer/Event Counter Input Clock Source
The Timer/Event Counter clock source can originate from various sources, an internal clock or an
external pin. The internal clock source is used when the timer is in the timer mode or in the pulse width
capture mode. For the Timer/Event Counter 0, this internal clock source is first divided by a prescaler,
the division ratio of which is conditioned by the Timer Control Register bits T0PSC0~T0PSC2. The
internal clock source can be derived from the system clock fSYS or the LXT oscillator for Timer/Event
Counter 0 or from the instruction clock fSYS/4 or the LXT oscillator for Timer/Event Counter 1 selected
by the clock selection bit TnS in the control register TMRnC.
An external clock source is used when the Timer/Event Counter is in the event counting mode, the
clock source being provided on an external timer pin TCn. Depending upon the condition of the TnEG
bit, each high to low, or low to high transition on the external timer pin will increment the counter by
one.
Timer Registers - TMR0, TMR1
The timer register is a special function register located in the Special Purpose Data Memory and is the
place where the actual timer value is stored and the register is known as TMRn. The value in the timer
register increases by one each time an internal clock pulse is received or an external transition occurs
on the external timer pin. The timer will count from the initial value loaded by the preload register to
the full count of FFH at which point the timer overflows and an internal interrupt signal is generated.
The timer value will be reset with the initial preload register value and continue counting.
To achieve a maximum full range count of FFH, the preload register must first be cleared to all zeros. It
should be noted that after power-on, the preload register will be in an unknown condition. Note that if
the Timer/Event Counter is switched off and data is written to its preload register, this data will be
immediately written into the actual timer register. However, if the Timer/Event Counter is enabled and
counting, any new data written into the preload data register during this period will remain in the
preload register and will only be written into the timer register the next time an overflow occurs.
Rev. 1.10
57
October 23, 2012
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