HT66F25D View Datasheet(PDF) - Holtek Semiconductor
Part Name
Description
MFG CO.
'HT66F25D' PDF : 177 Pages View PDF
A/D Flash Type 8-bit MCU with EEPROM
HT66F24D/HT66F25D
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 the 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 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. If a WDT
time-out occurs, it will set TO flag and cause 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.
Programming Considerations
The HXT and LXT oscillators both use the same SST counter. For example, if the system is woken
up from the SLEEP0 Mode and both the HXT and LXT oscillators need to start-up from an off state.
The LXT oscillator uses the SST counter after HXT oscillator has finished its SST period.
If the device is woken up from the SLEEP0 Mode to the NORMAL Mode, the high speed system
oscillator needs an SST period. The device will execute first instruction after the HTO bit is set to 1.
At this time, the LXT oscillator may not be stability if fSUB is from LXT oscillator. The same situation
occurs in the power-on state. The LXT oscillator is not ready yet when the first instruction is executed.
Rev. 1.10
49
March 25, 2013
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