Holtek BS66F340 - Standby Current Considerations; Wake-Up

Rev. 1.60 78 August 20, 2019 Rev. 1.60 79 August 20, 2019
BS66F340/BS66F350/BS66F360/BS66F370
Touch A/D Flash MCU with LED Driver
BS66F340/BS66F350/BS66F360/BS66F370
Touch A/D Flash MCU with LED Driver
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 and IDLE2 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 xed
high or low level as any oating 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 LIRC oscillator has enabled.
In the IDLE1 and IDLE 2 Mode the high speed oscillator is on, if the peripheral function clock
source is derived from the high speed oscillator, the additional standby current will also be perhaps
in the order of several hundred micro-amps.
Wake-up
To minimise power consumption the device can enter the SLEEP or any IDLE Mode, where the
CPU will be switched off. However, when the device is woken up again, it will take a considerable
time for the original system oscillator to restart, stablise and allow normal operation to resume.
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 overow
When the device executes the "HALT" instruction, the PDF ag will be set to 1. The PDF ag will
be cleared to 0 if the device experiences a system power-up or executes the clear Watchdog Timer
instruction. If the system is woken up by a WDT overow, a Watchdog Timer reset will be initiated
and the TO ag will be set to 1. The TO ag is set if a WDT time-out occurs and causes a wake-up
that only resets the Program Counter and Stack Pointer, other ags 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 rst 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 wukk rather be serviced later when the related interrupt is nally
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 ag is set high before entering the SLEEP or IDLE Mode, the wake-up function of
the related interrupt will be disabled.