Rev. 1.71
38
April 11, 2017
Rev. 1.71
39
April 11, 2017
HT66F002/HT66F0025/HT66F003/HT66F004
Cost-Effective A/D Flash MCU with EEPROM
HT66F002/HT66F0025/HT66F003/HT66F004
Cost-Effective A/D Flash MCU with EEPROM
Internal RC Oscillator – HIRC
The internal RC oscillator is a fully integrated system oscillator requiring no external components.
The internal RC oscillator has a fixed frequency of
8
MHz. Device trimming during the
manufacturing process and the inclusion of internal frequency compensation circuits are used to
ensure that the influence of the power supply voltage, temperature and process variations on the
oscillation frequency are minimised. As a result, at a power supply of 5V and at temperature of 25°C
degrees, the fixed oscillation frequency of the HIRC will have a tolerance within 2%.
Internal 32kHz Oscillator – LIRC
The
i
nternal 32kHz System Oscillator is the low frequency oscillator. It is a fully integrated
RC oscillator with a typical frequency of 32kHz at 5V, requiring no external components for its
implementation. Device trimming during the manufacturing process and the inclusion of internal
frequency compensation circuits are used to ensure that the influence of the power supply voltage,
temperature and process variations on the oscillation frequency are minimised.
Supplementary Oscillator
The low speed oscillator,
in
addition to providing
a
system clock source is also used to provide
a
clock source to two other device functions. These
are
the Watchdog Timer and the Time Base
Interrupts.
Operating Modes and System Clocks
Present day applications require that their microcontrollers have high performance but often still
demand that they consume as little power as possible, conflicting requirements that are especially
true in battery powered portable applications. The fast clocks required for high performance will
by their nature increase current consumption and of course vice-versa, lower speed clocks reduce
current consumption. As Holtek has provided these devices with both high and low speed clock
sources and the means to switch between them dynamically, the user can optimise the operation of
their microcontroller to achieve the best performance/power ratio.
System Clocks
These devices have two different clock sources for both the CPU and peripheral function operation.
By providing the user with clock options using register programming, a clock system can be
configured to obtain maximum application performance.
The main system clock, can come from either a high frequency, f
H
, or a low frequency, f
L
, and is
selected using the HLCLK bit and CKS2~CKS0 bits in the SMOD register. The high speed system
clock can be sourced from HIRC oscillator. The low speed system clock source can be sourced from
the internal clock f
L
. The other choice, which is a divided version of the high speed system oscillator
has a range of f
H
/2~f
H
/64.
There is one additional internal clock for the peripheral circuits, the Time Base clock, f
TBC
. f
TBC
is
sourced from the LIRC oscillators. The f
TBC
clock is used as a source for the Time Base interrupt
functions and for the TMs.
