HT68F14 HOLTEK [Holtek Semiconductor Inc], HT68F14 Datasheet - Page 29

• Manufacturer Part Number: HT68F14
• Description: Enhanced I/O Flash Type MCU
• Manufacturer: HOLTEK [Holtek Semiconductor Inc]

HT68F13/HT68F14/HT68F15
Enhanced I/O Flash Type MCU
Rev. 1.10
External RC Oscillator - ERC
Internal RC Oscillator - HIRC
Internal 32kHz Oscillator - LIRC
Supplementary Oscillator
Using the ERC oscillator only requires that a resistor, with a value between 24kW and 2.4MW, is
connected between OSC1 and V
a low cost oscillator configuration. It is only the external resistor that determines the oscillation
frequency; the external capacitor has no influence over the frequency and is connected for stability
purposes only. 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 resistance/
frequency reference point, it can be noted that with an external 120kW resistor connected and with a
5V voltage power supply and temperature of 25°C degrees, the oscillator will have a frequency of
8MHz within a tolerance of 2%. Here only the OSC1 pin is used, which is shared with I/O pin PB1,
leaving pin PB2 free for use as a normal I/O pin.
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 PB1 and PB2 are free for use as normal I/O pins.
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 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. As a result, at a power supply of 5V and at a temperature of 25¢J degrees, the fixed
oscillation frequency of 32kHz will have a tolerance within 10%.
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.
DD
, and a capacitor is connected between OSC1 and ground, providing
External RC Oscillator - ERC
29
February 9, 2011