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HT82B40R Datasheet(PDF) 27 Page - Holtek Semiconductor Inc |
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HT82B40R Datasheet(HTML) 27 Page - Holtek Semiconductor Inc |
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27 / 54 page  HT82B40R/HT82B40A Rev. 1.70 27 November 5, 2014 Power Down Mode and Wake-up Power Down Mode All of the Holtek microcontrollers have the ability to enter a Power Down Mode. When the device enters this mode, the normal operating current, will be reduced to an ex- tremely low standby current level. This occurs because when the device enters the Power Down Mode, the sys- tem oscillator is stopped which reduces the power con- sumption to extremely low levels, however, as the device maintains its present internal condition, it can be woken up at a later stage and continue running, without requiring a full reset. This feature is extremely important in applica- tion areas where the microcontroller must have its power supply constantly maintained to keep the device in a known condition but where the power supply capacity is limited such as in battery applications. Entering the Power Down Mode There is only one way for the device to enter the Power Down Mode and that is to execute the ²HALT² instruc- tion in the application program. When this instruction is executed, the following will occur: · The system oscillator will stop running and the appli- cation 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 if the WDT clock source is selected to come from the WDT or RTC oscillator. The WDT will stop if its clock source originates from the system clock. · The I/O ports will maintain their present condition. · 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 Power Down Mode is to keep the current consumption of the microcontroller to as low a value as possible, perhaps only in the order of several micro-amps, there are other considerations which must also be taken into account by the circuit de- signer 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 con- nected to either a fixed high or low level as any floating input pins could create internal oscillations and result in increased current consumption. 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 con- nected only to external circuits that do not draw current, such as other CMOS inputs. If the configuration options have enabled the Watchdog Timer internal oscillator then this will continue to run when in the Power Down Mode and will thus consume some power. For power sensitive applications it may be therefore preferable to use the system clock source for the Watchdog Timer. Wake-up After the system enters the Power Down Mode, it can be woken up from one of various sources listed as follows: · An external reset · An external falling edge on Port · A system interrupt · A WDT overflow If the system is woken up by an external reset, the de- vice will experience a full system reset, however, 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 ac- tual source of the wake-up can be determined by exam- ining 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 ²HALT² 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. Each pin can be setup via an individual configuration op- tion 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 ²HALT² instruction. If the system is woken up by an interrupt, then two possi- ble 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 exe- cution at the instruction following the ²HALT² instruction. In this situation, the interrupt which woke-up the device will not be immediately serviced, but will rather be ser- viced 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 to ²1² be- fore entering the Power Down Mode, the wake-up func- tion of the related interrupt will be disabled. |
Número de pieza similar - HT82B40R_14 |
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Descripción similar - HT82B40R_14 |
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