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HT46R003B
Cost-Effective A/D 8-bit OTP MCU
HT46R003B
Cost-Effective A/D 8-bit OTP MCU
Power Down Mode and Wake-up
Power Down Mode
All of the Holtek microcontrollers have the ability to enter a Power Down Mode, also known as the
HALT Mode or Sleep Mode. When the device enters this mode, the normal operating current will
be reduced to an extremely low standby current level. This occurs because when the device enters
the Power Down Mode, the system oscillator is stopped which reduces the power consumption
to extremely low levels. However, as the device maintains its present internal condition, they can
be woken up at a later stage and continue running, without requiring a full reset. This feature is
extremely important in application areas where the MCUs must have their power supply constantly
maintained to keep the device in a known condition.
Entering the Power Down Mode
There is only one way for the device to enter the Power Down Mode and that is to execute the
“HALT” instruction in the application program. When this instruction is executed, the following will
occur:
• The system oscillator will stop running and the application program will stop at the “HALT”
instruction.
• The Data Memory contents and registers will maintain their present condition.
• The WDT will be cleared and resume counting.
• The I/O ports will maintain their present condition.
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 Mode is to keep the current consumption of the
MCU to as low a value as possible, perhaps only in the order of several micro-amps, there are
other considerations which must also be taken into account by the circuit designer if the power
consumption is to be minimized.
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. Care must also be taken with the loads,
which are connected to I/O pins, which are set 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.
Wake-up
After the system enters the Sleep 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