HT68F20 Datasheet, PDF (37/210 Pages) Holtek Semiconductor Inc – Enhanced I/O Flash Type MCU 8-Bit MCU with EEPROM

HT68F20/HT68F30/HT68F40/HT68F50/HT68F60
Together with f_SYS/4 it is also used as one of the clock
sources for the Watchdog timer. The f_TBC clock is used
as a source for the Time Base interrupt functions and for
the TMs.
System Operation Modes
There are six different modes of operation for the
microcontroller, each one with its own special character-
istics and which can be chosen according to the specific
performance and power requirements of the applica-
tion. 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.
Operation Mode
NORMAL Mode
SLOW Mode
IDLE0 Mode
IDLE1 Mode
SLEEP0 Mode
SLEEP1 Mode
CPU
On
On
Off
Off
Off
Off
Description
f_SYS
f_H~ f_H/64
f_L
Off
f_SUB
f_S
f_TBC
On
On
On
On
On
On
On
On/Off
On
On
On
On
On
Off
Off
Off
Off
Off
On
On
Off
· NORMAL Mode
As the name suggests this is one of the main operat-
ing modes where the microcontroller has all of its
functions operational and where the system clock is
provided by one of the high speed oscillators. This
mode operates allowing the microcontroller to operate
normally with a clock source will come from one of the
high speed oscillators, either the HXT, ERC or HIRC
oscillators. The high speed oscillator will however first
be divided by a ratio ranging from 1 to 64, the actual
ratio being selected by the CKS2~LCKS0 and HLCLK
bits in the SMOD register. Although a high speed os-
cillator is used, running the microcontroller at a di-
vided clock ratio reduces the operating current.
· _{SLOW Mode}
This is also a mode where the microcontroller oper-
ates normally although now with a slower speed clock
source. The clock source used will be from one of the
low speed oscillators, either the LXT or the LIRC.
Running the microcontroller in this mode allows it to
run with much lower operating currents. In the SLOW
Mode, the f_H is off.
· _{SLEEP0 Mode}
The SLEEP Mode is entered when an HALT instruc-
tion is executed and when the IDLEN bit in the SMOD
register is low. In the SLEEP0 mode the CPU will be
stopped, and the f_SUB and f_S clocks will be stopped too,
and the Watchdog Timer function is disabled. In this
mode, the LVDEN is must set to ²0². If the LVDEN is
set to ²1², it won¢t enter the SLEEP0 Mode.
· _{SLEEP1 Mode}
The SLEEP Mode is entered when an HALT instruc-
tion is executed and when the IDLEN bit in the SMOD
register is low. In the SLEEP1 mode the CPU will be
stopped. However the f_SUB and f_S clocks will continue
to operate if the LVDEN is ²1² or the Watchdog Timer
function is enabled and if its clock source is chosen
via configuration option to come from the f_SUB.
· IDLE0 Mode
The IDLE0 Mode is entered when a HALT instruction
is executed and when the IDLEN bit in the SMOD reg-
ister is high and the FSYSON bit in the WDTC register
is low. In the IDLE0 Mode the system oscillator will be
inhibited from driving the CPU but some peripheral
functions will remain operational such as the Watch-
dog Timer, TMs and SIM. In the IDLE0 Mode, the sys-
tem oscillator will be stopped. In the IDLE0 Mode the
Watchdog Timer clock, f_S, will either be on or off de-
pending upon the f_S clock source. If the source is
f_SYS/4 then the f_S clock will be off, and if the source co-
mes from f_SUB then f_S will be on.
· _{IDLE1 Mode}
The IDLE1 Mode is entered when an HALT instruction
is executed and when the IDLEN bit in the SMOD reg-
ister is high and the FSYSON bit in the WDTC register
is high. In the IDLE1 Mode the system oscillator will be
inhibited from driving the CPU but may continue to
provide a clock source to keep some peripheral func-
tions operational such as the Watchdog Timer, TMs
and SIM. In the IDLE1 Mode, the system oscillator will
continue to run, and this system oscillator may be high
speed or low speed system oscillator. In the IDLE1
Mode the Watchdog Timer clock, f_S, will be on. If the
source is f_SYS/4 then the f_S clock will be on, and if the
source comes from f_SUB then f_S will be on.
Rev. 1.00
37
November 3, 2009