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Rev. 1.00
44
October 26, 2018
Rev. 1.00
45
October 26, 2018
BS86DH12C
High Voltage Touch A/D Flash MCU with HVIO
BS86DH12C
High Voltage Touch A/D Flash MCU with HVIO
Operating Modes and System Clocks
Present day applications require that their microcontrollers have high performance but often still
demand that they consume as little power as possible, conflicting requirements that are especially
true in battery powered portable applications. The fast clocks required for high performance will
by their nature increase current consumption and of course vice versa, lower speed clocks reduce
current consumption. As Holtek has provided the device with both high and low speed clock sources
and the means to switch between them dynamically, the user can optimise the operation of their
microcontroller to achieve the best performance/power ratio.
System Clocks
The device has many different clock sources for both the CPU and peripheral function operation. By
providing the user with a wide range of clock options using register programming, a clock system
can be configured to obtain maximum application performance.
The main system clock can come from a high frequency f
H
or low frequency f
SUB
source, and is
selected using the CKS2~CKS0 bits in the SCC register. The high speed system clock is sourced
from the HIRC oscillator. The low speed system clock source can be sourced from the internal clock
f
SUB
. If f
SUB
is selected then it can be sourced by either the LXT or LIRC oscillator, selected via
configuring the FSS bit in the SCC register. The other choice, which is a divided version of the high
speed system oscillator has a range of f
H
/2~f
H
/64.
High Speed
Oscillator
Prescaler
HIRC
f
H
f
H
/2
f
H
/4
f
H
/8
f
H
/16
f
H
/32
f
H
/64
CKS2~CKS0
f
SYS
LXT
Low Speed
Oscillators
LIRC
FSS
HIRCEN
SLEEP
IDLE2
SLEEP
f
SUB
f
SUB
f
SUB
f
SYS
/4
f
SYS
CLKSEL[1:0]
f
PSC
Prescaler
WDT
f
LIRC
Time Base
Device Clock Configurations
Note: When the system clock source f
SYS
is switched to f
SUB
from f
H
, the high speed oscillator can be stopped to
conserve the power or continue to oscillate to provide the clock source, f
H
~ f
H
/64, for peripheral circuits to
use, which is determined by configuring the corresponding high speed oscillator enable control bit.