HT45F4M View Datasheet(PDF) - Holtek Semiconductor

Part Name

Description

Manufacturer

HT45F4M

Lithium Battery Backup Power ASSP MCU

Holtek Semiconductor 

HT45F4M

Lithium Battery Backup Power ASSP MCU

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. 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 falling edge on Port A

• A system interrupt

• A WDT overflow

If the device is woken up by a WDT overflow, a Watchdog Timer reset will be initiated. The actual

source of the wake-up can be determined by examining the TO and PDF flags. The PDF flag is

cleared by a system power-up or executing the clear Watchdog Timer instructions and is set when

executing the “HALT” instruction. The TO flag is set if a WDT time-out occurs, and causes a wake-

up that only resets 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 “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.

Rev. 1.10

40

January 15, 2013

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