BH66F2470 Datasheet, PDF (54/223 Pages) Holtek Semiconductor Inc – Glucose Meter Flash MCU

BH66F2470
Glucose Meter 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 4MHz, 8MHz and 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. Note that if this internal system clock option
is selected, as it requires no external pins for its operation, I/O pins PA3 and PA4 are free for use as
normal I/O pins.
External 32.768kHz Crystal Oscillator – LXT
The External 32.768 kHz 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.
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.
The pin-shared software control bits determine if the XT1/XT2 pins are used for the LXT oscillator
or as I/O or other pin-shared functional pins.
• If the LXT oscillator is not used for any clock source, the XT1/XT2 pins can be used as normal I/O
or other pin-shared functional 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. 1.00
54
March 15, 2017