Inte�Nal Rc Oscillato� - Hirc; Exte�Nal 3�.�6�Khz C - Holtek BS83B24C Manual

High Speed
Oscillato�
HIRCEN
HIRC
Low Speed
Oscillato�s
LXTEN
LXT
LIRC
Internal 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 8/12/16 MHz, which is 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. As a result, at a power supply of 3V or 5V and at a temperature
of 25°C degrees, the selected trimmed oscillation frequency will have a tolerance within 1%.
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 a software control bit, FSS. 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.
After the LXT oscillator is enabled by setting the LXTEN bit to 1, 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, R
Rev. 1.00
IDLE0
SLEEP
�SS
f
SUB
IDLE�
SLEEP
f
LIRC
System Clock Configurations
and the pull-high resister, R
P
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BS83B24C/BS83C40C
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