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Rev. 1.20
40
November 20, 2019
Rev. 1.20
41
November 20, 2019
HT66F2740
12V High Current Flash MCU
HT66F2740
12V High Current Flash MCU
Internal High Speed RC Oscillator – HIRC
The internal RC oscillator is a fully integrated system oscillator requiring no external components.
The internal RC oscillator has three fixed frequencies of 8MHz, 12MHz and 16MHz, which are
selected using a configuration option. The HIRC1~HIRC0 bits in the HIRCC register must also
be setup to match the selected configuration option frequency. Setting up these bits is necessary to
ensure that the HIRC frequency accuracy specified in the A.C. Characteristics is achieved.
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.
Internal 32kHz Oscillator – LIRC
The Internal 32kHz System Oscillator is the low frequency oscillator. It is a fully integrated RC
oscillator with a typical frequency of 32kHz at full voltage range, requiring no external components
for its implementation.
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 the device 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
The device has many different clock sources for both the CPU and peripheral function operation.
By providing the user with a wide range of clock options using configuration options and 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 low frequency f
SUB
source,
and is selected using the CKS2~CKS0 bits in the SCC register. The high speed system clock can
be sourced from the HIRC oscillator. The low speed system clock source can be sourced from the
LIRC oscillator. The other choice, which is a divided version of the high speed system oscillator has
a range of f
H
/2~ f
H
/64.