HT45F23/HT45F43
8-Bit Flash MCU with Op Amps & Comparators
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In the status register, the Power Down flag, PDF, will be set and the Watchdog time-out flag, TO,
will be cleared.
Standby Current Considerations
As the main reason for entering the SLEEP or IDLE Mode is to keep the current consumption of the
device to as low a value as possible, perhaps only in the order of several micro-amps except in the
IDLE1 Mode, there are other considerations which must also be taken into account by the circuit
designer if the power consumption is to be minimised. Special attention must be made to the I/O pins
on the device. All high-impedance input pins must be connected to either a fixed high or low level as
any floating input pins could create internal oscillations and result in increased current consumption.
This also applies to devices which have different package types, as there may be unbonbed pins. These
must either be setup as outputs or if setup as inputs must have pull-high resistors connected.
Care must also be taken with the loads, which are connected to I/O pins, which are setup as outputs.
These should be placed in a condition in which minimum current is drawn or connected only to
external circuits that do not draw current, such as other CMOS inputs. Also note that additional
standby current will also be required if the configuration options have enabled the LXT or LIRC
oscillator.
In the IDLE1 Mode the system oscillator is on, if the system oscillator is from the high speed system
oscillator, the additional standby current will also be perhaps in the order of several hundred
micro-amps
Wake-up
After the system enters the SLEEP or IDLE Mode, it can be woken up from one of various sources
listed as follows:
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An external reset
·
·
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An external falling edge on Port A
A system interrupt
A WDT overflow
If the system is woken up by an external reset, the device will experience a full system reset, how-
ever, if the device is woken up by a WDT overflow, a Watchdog Timer reset will be initiated. Al-
though both of these wake-up methods will initiate a reset operation, the actual source of the
wake-up can be determined by examining the TO and PDF flags. The PDF flag is cleared by a sys-
tem power-up or executing the clear Watchdog Timer instructions and is set when executing the
²HALT² instruction. The TO flag is set if a WDT time-out occurs, and causes a wake-up that only re-
sets the Program Counter and Stack Pointer, the other flags remain in their original status.
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 ²HALT² 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
²HALT² 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.
Rev. 1.20
48
September 15, 2011
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
