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Rev. 1.00
52
October 26, 2018
Rev. 1.00
53
October 26, 2018
BS86DH12C
High Voltage Touch A/D Flash MCU with HVIO
BS86DH12C
High Voltage Touch A/D Flash MCU with HVIO
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 fixed high or
low level as any floating input pins could create internal oscillations and result in increased current
consumption. This also applies to the device which has different package types, as there may be
unbonded pins. These must either be set as outputs or if set 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 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. Also note that additional
standby current will also be required if the LXT or LIRC oscillator has enabled.
In the IDLE1 and IDLE2 Mode the high speed oscillator is on and if the system clock 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
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, stabilise 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 overflow
When the device executes the “HALT” instruction, it will enter the SLEEP or IDLE mode and the
PDF flag will be set high. The PDF flag 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
overflow, a Watchdog Time-out hardware reset will be initiated and the TO flag will be set to 1. 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, other flags remain in their original status.
Each pin on Port A can be set using the PAWU register to permit a negative transition on the pin
to wake-up the system. When 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.