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HT82B40R Fiches technique(PDF) 16 Page - Holtek Semiconductor Inc

No de pièce HT82B40R
Description  I/O 8-Bit MCU with USB Interface
Download  54 Pages
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Fabricant  HOLTEK [Holtek Semiconductor Inc]
Site Internet  http://www.holtek.com
Logo HOLTEK - Holtek Semiconductor Inc

HT82B40R Fiches technique(HTML) 16 Page - Holtek Semiconductor Inc

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HT82B40R/HT82B40A
Rev. 1.70
16
November 5, 2014
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. This device contains two
count-up timers of 8-bit and 16-bit capacities respec-
tively. As each timer has three different operating
modes, they can be configured to operate as a general
timer, an external event counter or as a pulse width
measurement device.
There are two types of registers related to the
Timer/Event Counters. The first is the register that con-
tains the actual value of the Timer/Event Counter and
into which an initial value can be preloaded, and is
known as TMR0, TMR1H or TMR1L. Reading from this
register retrieves the contents of the Timer/Event Coun-
ter. 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,
and has the name TMR0C or TMR1C. This device can
have the timer clocks configured to come from the inter-
nal clock sources. In addition, the timer clock source can
also be configured to come from the external timer pins.
The external clock source is used when the Timer/Event
Counter is in the event counting mode, the clock source
being provided on the external timer pin. The pin has the
name TMR0 or TMR1 and is pin-shared with an I/O pin.
Depending upon the condition of the T0E or T1E bit in
the Timer Control Register, each high to low, or low to
high transition on the external timer input pin will incre-
ment the Timer/Event Counter by one.
Configuring the Timer/Event Counter Input Clock
Source
The Timer/Event Counter
¢s clock can originate from var-
ious sources. The system clock source is used when the
Timer/Event Counter 0 is in the timer mode or in the
pulse width measurement mode. The instruction clock
source (system clock source divided by 4) is used when
the Timer/Event Counter 1 is in the timer mode or in the
pulse width measurement mode. The external clock
source is used when the Timer/Event Counter is in the
event counting mode, the clock source being provided
on the external timer pin, TMR0 or TMR1. 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 Register
- TMR0, TMR1L/TMR1H
The timer registers are special function registers located
in the Special Purpose RAM Data Memory and are the
places where the actual timer values are stored. For
8-bit Timer/Event Counter 0, this register is known as
TMR0. For 16-bit Timer/Event Counter 1, the timer reg-
isters are known as TMR1L and TMR1H. The value in
the timer registers increases by one each time an inter-
nal clock pulse is received or an external transition oc-
curs on the external timer pin. The timer will count from
the initial value loaded by the preload register to the full
count of FFH for the 8-bit timer or FFFFH for the 16-bit
timer at which point the timer overflows and an internal
interrupt signal is generated. The timer value will then
be reset with the initial preload register value and con-
tinue counting.
To achieve a maximum full range count of FFH for the
8-bit timer or FFFFH for the 16-bit timer, the preload reg-
isters 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
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 re-
main in the preload registers and will only be written into
the timer registers the next time an overflow occurs.
For the 16-bit Timer/Event Counter which has both low
byte and high byte timer registers, accessing these reg-
isters is carried out in a specific way. It must be note
when using instructions to preload data into the low byte
timer register, namely TMR1L, the data will only be
placed in a low byte buffer and not directly into the low
byte timer register. The actual transfer of the data into
the low byte timer register is only carried out when a
write to its associated high byte timer register, namely
TMR1H, is executed. On the other hand, using instruc-
tions to preload data into the high byte timer register will
result in the data being directly written to the high byte
timer register. At the same time the data in the low byte
buffer will be transferred into its associated low byte
timer register. For this reason, the low byte timer register
should be written first when preloading data into the
16-bit timer registers. It must also be noted that to read
the contents of the low byte timer register, a read to the
high byte timer register must be executed first to latch
the contents of the low byte timer register into its associ-
ated low byte buffer. After this has been done, the low
byte timer register can be read in the normal way. Note
that reading the low byte timer register will result in read-
ing the previously latched contents of the low byte buffer
and not the actual contents of the low byte timer register.
Timer Control Register
- TMR0C/TMR1C
The flexible features of the Holtek microcontroller
Timer/Event Counters enable them to operate in three
different modes, the options of which are determined by
the contents of their respective control register. For de-
vices are two timer control registers known as TMR0C,
TMR1C . It is the timer control register together with its
corresponding timer registers that control the full opera-
tion of the Timer/Event Counters. Before the timers can
be used, it is essential that the appropriate timer control


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