Rev. 1.10
38
November 26, 2019
Rev. 1.10
39
November 26, 2019
HT68FB240
USB Low Speed Flash MCU
High Speed
Oscillator
HIRC
LIRC
f
H
6-stage Prescaler
HLCLK,
CKS2~CKS0 bits
f
H
/2
f
H
/4
f
H
/8
f
H
/16
f
H
/32
f
H
/64
f
SUB
÷2
SYSCLK
Bit
6MHz
USBCKEN bit
SYSCLK
To USBCK
Circuits
f
SYS
WDT
f
L
Low Speed
Oscillator
System Clock Configuration
Note: When the system clock source f
SYS
is switched to f
L
from f
H
, the high speed oscillation will
stop to conserve the power. Thus there is no f
H
~f
H
/64 for peripheral circuit to use.
System Operation Modes
There are six different modes of operation for the microcontroller, each one with its own
special characteristics and which can be chosen according to the specific performance and
power requirements of the application. There are two modes allowing normal operation of the
microcontroller, the NORMAL Mode and SLOW Mode. The remaining four modes, the SLEEP0,
SLEEP1, IDLE0 and IDLE1 Mode are used when the microcontroller CPU is switched off to
conserve power.
Operating Mode
Description
CPU
f
SYS
f
SUB
NORMAL Mode
on
f
H
~f
H
/64
on
SLOW Mode
on
f
L
on
IDLE0 Mode
off
off
on
IDLE1 Mode
off
on
on
SLEEP0 Mode
off
off
off
SLEEP1 Mode
off
off
on