HT45F23 datasheet(37/152 Pages) HOLTEK

37 / 152 page

External RC Oscillator

- ERC

Using the ERC oscillator only requires that a resistor, with a value between 56k

W and 2.4MW,is

connected between OSC1 and VDD, and a capacitor is connected between OSC1 and ground,

providing 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 150k

W resistor connected

and with a 5V voltage power supply and temperature of 25

°C degrees, the oscillator will have a

frequency of 4MHz within a tolerance of 2%. Here only the OSC1 pin is used, which is shared with I/O

pin PC0, leaving pin PC1 free for use as a normal I/O pin.

External Oscillator

- EC

The system clock can also be supplied by an externally supplied clock giving users a method of

synchronising their external hardware to the microcontroller operation. This is selected using a

configuration option and supplying the clock on pin OSC1. Pin OSC2 should be left floating if the

external oscillator is used. The internal oscillator circuit contains a filter circuit to reduce the

possibility of erratic operation due to noise on the oscillator pin, however as the filter circuit consumes

a certain amount of power, a configuration option exists to turn this filter off. Not using the internal

filter should be considered in power sensitive applications and where the externally supplied clock is

of a high integrity and supplied by a low impedance source.

Internal RC Oscillator

- HIRC

The internal RC oscillator is a fully integrated system oscillator requiring no external components. The

internal RC oscillator has four fixed frequencies of either 910kHzm 2MHz, 4MHz or 8MHz. 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 910kHzm 2MHz, 4MHz or

8MHz 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 PC0 and PC1 are free for use as normal I/O pins.

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 32.768kHz and

requires a 32.768kHz crystal to be connected between pins XT1 and XT2. The external resistor and

capacitor components connected to the 32.768kHz 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.

HT45F23/HT45F43

8-Bit Flash MCU with Op Amps & Comparators

Rev. 1.20

September 15, 2011

P C 0 / O S C 1

2 0 p F

V D D

R O S C

P C 1 / O S C 2

External RC Oscillator

- ERC

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