Rev. 1.21
44
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Rev. 1.21
45
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HT66F488/HT66F489
A/D Flash MCU with EEPROM
HT66F488/HT66F489
A/D Flash MCU with EEPROM
Entering the IDLE1 Mode
There is only one way for the device to enter the IDLE1 Mode and that is to execute the “HALT”
instruction in the application program with the IDLEN bit in SMOD register equal to “1” and the
FSYSON bit in CTRL register equal to “1”. When this instruction is executed under the conditions
described above, the following will occur:
• The system clock and Time Base clock and
f
SUB
will be on 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 conditions.
• 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. 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. Although
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 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.