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Rev. 1.21
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HT66F488/HT66F489
A/D Flash MCU with EEPROM
HT66F488/HT66F489
A/D Flash MCU with EEPROM
Each pin on Port A can be setup using the PAWU register to permit a negative transition on the pin
to wake-up the system. When a Port A pin wake-up occurs, the program will resume execution at
the instruction following the “HALT” instruction. If the system is woken up by an interrupt, then
two possible situations may occur. The first is where the related interrupt is disabled or the interrupt
is enabled but the stack is full, in which case the program will resume execution at the instruction
following the “HALT” instruction. In this situation, the interrupt which woke-up the device will not
be immediately serviced, but will rather be serviced later when the related interrupt is finally enabled
or when a stack level becomes free. The other situation is where the related interrupt is enabled and
the stack is not full, in which case the regular interrupt response takes place. If an interrupt request
flag is set high before entering the SLEEP or IDLE Mode, the wake-up function of the related
interrupt will be disabled.
Programming Considerations
The high speed and low speed oscillators both use the same SST counter. For example, if the system
is woken up from the SLEEP Mode and the HIRC oscillators need to start-up from an off state.
• If the device is woken up from the SLEEP Mode to NORMAL Mode, and the system clock
source is from HXT oscillator and FSTEN is “1”, the system clock can be switched to the LIRC
or LXT oscillator after wake up.
• There are peripheral functions, such as TMs, for which the f
SYS
is used. If the system clock source
is switched from f
H
to f
L
, the clock source to the peripheral functions mentioned above will
change accordingly.
Watchdog Timer
The Watchdog Timer is provided to prevent program malfunctions or sequences from jumping to
unknown locations, due to certain uncontrollable external events such as electrical noise.
Watchdog Timer Clock Source
The Watchdog Timer clock source is provided by the
f
SUB
clock. The f
SUB
clock can be sourced from
either the LIRC or LXT oscillator selected by a configuration option. The LIRC internal oscillator
has an approximate frequency of 32kHz and this specified internal clock period can vary with V
DD
,
temperature and process variations. The LXT oscillator is supplied by an external 32.768 kHz
crystal. The Watchdog Timer source clock is then subdivided by a ratio of 2
8
to 2
18
to give longer
timeouts, the actual value being chosen using the WS2~WS0 bits in the WDTC register.
Watchdog Timer Control Register
A single register, WDTC, controls the required timeout period as well as the enable or reset
operation.