BS85B12-3 Datasheet, PDF (45/182 Pages) Holtek Semiconductor Inc – Touch Key Flash Type 8-Bit MCU with LCD/LED Driver

BS85B12-3/BS85C20-3
Touch Key Flash MCU with LCD/LED Driver
Entering the IDLE0 Mode
There is only one way for the device to enter the IDLE0 Mode and that is to execute the ²HALT²
instruction in the application program with the IDLEN bit in SMOD register equal to ²1² and the
FSYSON bit in WDTC register equal to ²0². When this instruction is executed under the conditions
described above, the following will occur:
· The system clock will be stopped and the application program will stop at the ²HALT² instruction,
but the Time Base clock and f_LIRC clock will be on.
· 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.
Entering the IDLE1 Mode
There is only one way for the device to enter the IDLE1 Mode and that is to execute the ²HALT²
instruction in the application program with the IDLEN bit in SMOD register equal to ²1² and the
FSYSON bit in WDTC register equal to ²1². When this instruction is executed under the with conditions
described above, the following will occur:
· The system clock and f_LIRC clock will be on and the application program will stop at the ²HALT²
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.
Rev. 1.00
39
February 1, 2011