Rev. 1.10
40
November 26, 2019
Rev. 1.10
41
November 26, 2019
HT68FB240
USB Low Speed Flash MCU
Operating Mode Switching
The device can switch between operating modes dynamically allowing the user to select the best
performance/power ratio for the present task in hand. In this way microcontroller operations that
do not require high performance can be executed using slower clocks thus requiring less operating
current and prolonging battery life in portable applications.
In simple terms, Mode Switching between the NORMAL Mode and SLOW Mode is executed
using the HLCLK bit and CKS2~CKS0 bits in the SMOD register while Mode Switching from the
NORMAL/SLOW Modes to the SLEEP/IDLE Modes is executed via the HALT instruction. When
a HALT instruction is executed, whether the device enters the IDLE Mode or the SLEEP Mode is
determined by the condition of the IDLEN bit in the SMOD register and FSYSON in the CTRL
register.
When the HLCLK bit switches to a low level, which implies that clock source is switched from the
high speed clock source, f
H
, to the clock source, f
H
/2~f
H
/64 or f
L
. If the clock is from the f
L
, the high
speed clock source will stop running to conserve power. When this happens it must be noted that the
f
H
/16 and f
H
/64 internal clock sources will also stop running, which may affect the operation of other
internal functions such as the TMs. The accompanying flowchart shows what happens when the
device moves between the various operating modes.
