HT68F017 datasheet(32/116 Pages) HOLTEK

32 / 116 page

HT66F016/HT66F017/HT68F016/HT68F017

Rev. 1.00

May 14, 2012

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 bat-

tery powered portable applications. The fast clocks re-

quired 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 perfor-

mance/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 config-

uration options and register programming, a clock sys-

tem can be configured to obtain maximum application

performance.

The main system clock, can come from either a high fre-

quency, fH, or low frequency, fL, source, and is selected

using the HLCLK bit and CKS2~CKS0 bits in the SMOD

from either an HXT or HIRC oscillator, selected via a

configuration option. The low speed system clock

source can be sourced from internal clock fL. The other

choice, which is a divided version of the high speed sys-

tem oscillator has a range of fH/2~fH/64.

There are two additional internal clocks for the periph-

eral circuits, the substitute clock, fSUB, and the Time

Base clock, fTBC. Each of these internal clocks are

sourced by the LIRC oscillators. 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.

f H

f H / 6 4

f H / 3 2

f H / 1 6

f H / 8

f H / 4

f H / 2

6 - s t a g e P r e s c a l e r

f S U B

H i g h S p e e d O s c i l l a t i o n

C o n f i g u r a t i o n O p t i o n

f S Y S

H L C L K ,

C K S 2 ~ C K S 0 b i t s

F a s t W a k e - u p f r o m S L E E P M o d e o r

I D L E M o d e C o n t r o l ( f o r H X T o n l y )

f S C o n f i g u r a t i o n O p t i o n

T B C K

T i m e B a s e

W D T

f T B C

f S Y S / 4

f T B

f S Y S / 4

f S U B

f S

H i g h S p e e d

O s c i l l a t i o n

H X T

H I R C

L I R C

L o w S p e e d

O s c i l l a t i o n

f L

System Clock Configurations

Note:

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.

HT68F017 датащи(PDF) 32 Page - Holtek Semiconductor Inc

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