HT66F24D View Datasheet(PDF) - Holtek Semiconductor
Part Name
Description
MFG CO.
'HT66F24D' PDF : 177 Pages View PDF
A/D Flash Type 8-bit MCU with EEPROM
HT66F24D/HT66F25D
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 either 4MHz, 8MHz or 12MHz. 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 either 3V or
5V and at a temperature of 25°C degrees, the fixed oscillation frequency of 4MHz, 8MHz or 12MHz
will have a tolerance within 2%. Note that if this internal system clock option is selected, as it
requires no external pins for its operation, I/O pins PA6 and PA5 are free for use as normal I/O pins.
Internal 32kHz Oscillator – LIRC
The Internal 32kHz System Oscillator is one of the low frequency oscillator choices, which is
selected via configuration option. It is a fully integrated RC oscillator with a typical frequency of
32 kHz 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. As a result, at a power supply of 5V and at a temperature of
25°C degrees, the fixed oscillation frequency of 32 kHz will have a tolerance within 10%.
External 32.768kHz Crystal Oscillator – LXT
The External 32.768kHz Crystal System Oscillator is one of the low frequency oscillator choices,
which is selected via configuration option. This clock source has a fixed frequency of 32.768 kHz
and requires a 32.768 kHz crystal to be connected between pins XT1 and XT2. The external resistor
and capacitor components connected to the 32.768 kHz crystal are necessary to provide oscillation.
For applications where precise frequencies are essential, these components may be required to
provide frequency compensation due to different crystal manufacturing tolerances. During power-up
there is a time delay associated with the LXT oscillator waiting for it to start-up.
When the microcontroller enters the SLEEP or IDLE Mode, the system clock is switched off to stop
microcontroller activity and to conserve power. However, in many microcontroller applications it
may be necessary to keep the internal timers operational even when the microcontroller is in the
SLEEP or IDLE Mode. To do this, another clock, independent of the system clock, must be provided.
However, for some crystals, to ensure oscillation and accurate frequency generation, it is necessary
to add two small value external capacitors, C1 and C2. The exact values of C1 and C2 should be
selected in consultation with the crystal or resonator manufacturer’s specification. The external
parallel feedback resistor, Rp, is required.
Some configuration options determine if the XT1/XT2 pins are used for the LXT oscillator or as I/O
pins.
• If the LXT oscillator is not used for any clock source, the XT1/XT2 pins can be used as normal
I/O pins.
• If the LXT oscillator is used for any clock source, the 32.768 kHz crystal should be connected to
the XT1/XT2 pins.
Rev. 1.10
38
March 25, 2013
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