Rev. 1.20
48
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Rev. 1.20
49
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BS82B12A-3/BS82C16A-3/BS82D20A-3
Touch Key 8-Bit Flash MCU with LED/LCD Driver
BS82B12A-3/BS82C16A-3/BS82D20A-3
Touch Key 8-Bit Flash MCU with LED/LCD Driver
LXT Oscillator Low Power Function
The LXT oscillator can function in one of two modes, the Quick Start Mode and the Low Power
Mode. The mode selection is executed using the LXTLP bit in the CTRL register.
LXTLP Bit
LXT Mode
0
Q�ick Sta�t
1
Low-powe�
After power on, the LXTLP bit will be automatically cleared to zero ensuring that the LXT oscillator
is in the Quick Start operating mode. In the Quick Start Mode the LXT oscillator will power up
and stabilise quickly. However, after the LXT oscillator has fully powered up it can be placed
into the Low-power mode by setting the LXTLP bit high. The oscillator will continue to run but
with reduced current consumption, as the higher current consumption is only required during the
LXT oscillator start-up. In power sensitive applications, such as battery applications, where power
consumption must be kept to a minimum, it is therefore recommended that the application program
sets the LXTLP bit high about 2 seconds after power-on.
It should be noted that, no matter what condition the LXTLP bit is set to, the LXT oscillator will
always function normally, the only difference is that it will take more time to start up if in the Low-
power mode.
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 these devices 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 main system clock, can come from either a high frequency, f
H
, or low frequency, f
SUB
, source,
and is selected using the HLCLK bit and CKS2~CKS0 bits in the SMOD register. The high speed
system clock is sourced from the HIRC oscillator
.
The low speed system clock source can be sourced
from internal clock f
SUB
. Depending on the devices, if f
SUB
is selected then it is sourced by the LIRC
oscillator or can be sourced by either the LXT or LIRC oscillators, selected via a configuration
option. The other choice, which is a divided version of the high speed system oscillator has a range
of f
H
/2~f
H
/64.
Содержание BS82B12A-3
Страница 33: ...Rev 1 20 33 January 23 2015 BS82B12A 3 BS82C16A 3 BS82D20A 3 Touch Key 8 Bit Flash MCU with LED LCD Driver ...
Страница 34: ...Rev 1 20 34 January 23 2015 BS82B12A 3 BS82C16A 3 BS82D20A 3 Touch Key 8 Bit Flash MCU with LED LCD Driver ...
Страница 35: ...Rev 1 20 35 January 23 2015 BS82B12A 3 BS82C16A 3 BS82D20A 3 Touch Key 8 Bit Flash MCU with LED LCD Driver ...