HT45F43 datasheet(48/152 Pages) HOLTEK

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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:

· An external reset

· 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

September 15, 2011

HT45F23/HT45F43

8-Bit Flash MCU with Op Amps & Comparators

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