HT66F24D View Datasheet(PDF) - Holtek Semiconductor
Part Name
Description
MFG CO.
'HT66F24D' PDF : 177 Pages View PDF
A/D Flash Type 8-bit MCU with EEPROM
HT66F24D/HT66F25D
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 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 configuration options and register
programming, a clock system can be configured to obtain maximum application performance.
The main system clock can come from a high frequency fH or low frequency fL source and is selected
using the HLCLK bit and CKS2~CKS0 bits in the SMOD register. The high speed system clock can
be sourced from either a HXT or HIRC oscillator, selected via a configuration option. The low speed
system clock source can be sourced from internal clock fL. If fL is selected, then it can be sourced by
the LIRC oscillator. The other choice, which is a divided version of the high speed system oscillator
has a range of fH/2~fH/64.Note that when the system clock source fSYS is switched to fL from fH,
the high speed oscillation will stop to conserve the power. Thus there is no fH~fH/64 for peripheral
circuit to use.
There are two additional internal clocks for the peripheral circuits, the substitute clock, fSUB, and the
Time Base clock, fTBC. These internal clocks are sourced by the LIRC or LXT oscillator. The fSUB
clock is used to provide a substitute clock for the microcontroller just after a wake-up has occurred
to enable faster wake-up times. The fTBC clock is used as a source for the Time Base interrupt
functions and for the TMs.
Hig� Speed Os�illato�
HXT
fH
HIRC
Hig� Speed Os�illato�
Configu�ation Option
Low Speed Os�illato�
LXT
LIRC
fSUB Clo�k
Configu�ation Option
6-stage P�es�ale�
fH/�
fH/4
fH/8
fH/16
fH/��
fH/64
fSUB
HLCLK�
CKS�~CKS0 bits
fSUB
fSYS
Fast Wake-up f�om
SLEEP o� IDLE �ode
Cont�ol (fo� HXT only)
fSUB
Wat��dog Time�
fSUB
fSYS/4
fTB
Time Base
TBCK
Rev. 1.10
40
March 25, 2013
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