HT45F43 datasheet(61/152 Pages) HOLTEK

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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 one 8-bit and one 16-bit count-up timer. As

each timer has four different operating modes, they can be configured to operate as a general timer, an

external event counter, an internal event counter for comparator, or as a pulse width measurement

device. The provision of a prescaler to the clock circuitry of the 8-bit Timer/Event Counter also gives

added range to this timer.

There are two types of registers related to the Timer/Event Counters. The first are the registers that

contain the actual value of the Timer/Event Counter and into which an initial value can be preloaded.

Reading from these registers 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/Event Counter is to be used. The Timer/Event Counters can have the their clock configured

to come from an internal clock source. In addition, their clock source can also be configured to come

from an external timer pin.

Configuring the Timer/Event Counter Input Clock Source

The internal timer

¢s clock can originate from various sources. The system clock source is used when

the Timer/Event Counter is in the timer mode or in the pulse width measurement mode. For

Timer/Event Counter 0 this internal clock source is fSYS which is also divided by a prescaler, the

division ratio of which is conditioned by the Timer Control Register, TMR0C, bits T0PSC0~ T0PSC2.

For Timer/Event Counter 1 this internal clock source can be chosen from a combination of internal

clocks using a configuration option and the T1S bit in the TMR1C register.

An external clock source is used when the timer is in the event counting mode, the clock source being

provided on an external timer pin TC0 or TC1, depending upon which timer is used. Depending upon

the condition of the T0E or T1E bit, each high to low, or low to high transition on the external timer pin

will increment the counter by one.

Timer Registers

- TMR0, TMR1L, TMR1H

The timer registers are special function registers located in the Special Purpose Data Memory and is the

place where the actual timer value is stored. For the 8-bit Timer/Event Counter 0, this register is known as

TMR0. For 16-bit Timer/Event Counter 1, the timer registers are known as TMR1L and TMR1H. The

value in the timer registers 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

overflows and an internal interrupt signal is generated. The timer value will then be reset with the initial

preload register value and continue counting.

To achieve a maximum full range count of FFH for the 8-bit timer or FFFFH for the 16-bit timer, the

preload registers must first be cleared to all zeros. It should be noted that after power-on, the preload

is written to its preload registers, this data will be immediately written into the actual timer registers.

However, if the Timer/Event Counter is enabled and counting, any new data written into the preload

data registers during this period will remain in the preload registers and will only be written into the

timer registers the next time an overflow occurs.

HT45F23/HT45F43

8-Bit Flash MCU with Op Amps & Comparators

Rev. 1.20

September 15, 2011

HT45F43 Datasheet(PDF) 61 Page - Holtek Semiconductor Inc

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