
Rev. 1.21
44
�ove��e� ��� 2�1�
Rev. 1.21
45
�ove��e� ��� 2�1�
HT66F488/HT66F489
A/D Flash MCU with EEPROM
HT66F488/HT66F489
A/D Flash MCU with EEPROM
NORMAL Mode to SLOW1 Mode Switching
When running in the NORMAL Mode, which uses the high speed system oscillator, and therefore
consumes more power, the system clock can switch to run in the SLOW1 Mode by setting the
HLCLK bit to “0” and setting the CKS2~CKS0 bits to “010”, “011”, “100”, “101”, “110” or
“111” in the SMOD register.This will then use a divided clock of the high speed system oscillator
which can reduce the operating current. The SLOW1 Mode is still sourced from the HIRC or HXT
oscillator and therefore requires less time for full mode switching.
SLOW0 Mode to NORMAL Mode Switching
In SLOW0 Mode the system uses LIRC or LXT low speed system oscillator. To switch back to the
NORMAL Mode, where the high speed system oscillator is used, the HLCLK bit should be set to “1”.
As a certain amount of time will be required for the high frequency clock to stabilise, the status of
the HTO bit is checked. The amount of time required for high speed system oscillator stabilization
depends upon which high speed system oscillator type is used.
SLOW1 Mode to NORMAL Mode Switching
In SLOW1 Mode the system still uses high speed system oscillator. To switch back to the NORMAL
Mode, where also the high speed system oscillator is used, the HLCLK bit should be set to “1”. As
the two modes both use the high speed system oscillator, therefore requires less time for full mode
switching.
Entering the SLEEP Mode
There is only one way for the device to enter the SLEEP Mode and that is to execute the “HALT”
instruction in the application program with the IDLEN bit in SMOD register equal to “0” and the
WDT on. When this instruction is executed under the conditions described above, the following will
occur:
• The system clock and Time Base clock will be stopped and the application program will stop at
the “HALT” instruction, but the WDT will remain with the clock source coming from the f
SUB
clock.
• The Data Memory contents and registers will maintain their present condition.
• The WDT will be cleared and resume counting.
• The I/O ports will maintain their present conditions.
• In the status register, the Power Down flag, PDF, will be set and the Watchdog time-out flag, TO,
will be cleared.
Entering the IDLE0 Mode
There is only one way for the device to enter the IDLE0 Mode and that is to execute the “HALT”
instruction in the application program with the IDLEN bit in SMOD register equal to “1” and the
FSYSON bit in CTRL register equal to “0”. When this instruction is executed under the conditions
described above, the following will occur:
• The system clock will be stopped and the application program will stop at the “HALT” instruction,
but the Time Base clock
f
TBC
and the f
SUB
clock will be on.
• The Data Memory contents and registers will maintain their present condition.
• The WDT will be cleared and resume counting.
• The I/O ports will maintain their present conditions.
• In the status register, the Power Down flag, PDF, will be set and the Watchdog time-out flag, TO,
will be cleared.