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MS51
Nov. 28, 2019
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Rev 1.00
MS51
32K
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exit. It will automatically clear the IDL bit, terminate Idle mode, and the interrupt service routine (ISR)
will be executed. After using the RETI instruction to jump out of the ISR, execution of the program will
be the one following the instruction, which put the CPU into Idle mode. The second way to terminate
Idle mode is with any reset other than software reset. Remember that if Watchdog reset is used to exit
Idle mode, the WIDPD (WDCON.4) needs to be set 1 to let WDT keep running in Idle mode.
Power-Down Mode
6.2.2.3
Power-down mode is the lowest power state that the MS51 can enter. It remain the power
consumption as A ”Μa” level by stopping the system clock source. Both of CPU and peripheral
functions like Timers or UART are frozen. Flash memory is put into its stop mode. All activity is
completely stopped and the power consumption is reduced to the lowest possible value. The device
can be put into Power-down mode by writing 1 to bit PD (PCON.1). The instruction that does this
action will be the last instruction to be executed before the device enters Power-down mode. In the
Power-down mode, RAM maintains its content. The port pins output the values held by their own state
before Power-down respectively.
There are several ways to exit the MS51 from the Power-down mode. The first is with all resets except
software reset. Brown-out reset will also wake up CPU from Power-down mode. Be sure that brown-
out detection is enabled before the system enters Power-down. However, for least power
consumption, it is recommended to enable low power BOD in Power-down mode. Of course the
external pin reset and power-on reset will remove the Power-down status. After the external reset or
power-on reset. The CPU is initialized and start executing program code from the beginning.
The second way to wake the MS51 up from the Power-down mode is by an enabled external interrupt.
The trigger on the external pin will asynchronously restart the system clock. After oscillator is stable,
the device executes the interrupt service routine (ISR) for the corresponding external interrupt. After
the ISR is completed, the program execution returns to the instruction after the one, which puts the
device into Power-down mode and continues. Interrupts that allows to wake up CPU from Power-down
mode includes external interrupt
INT0
̅̅̅̅̅̅̅
and
INT1
̅̅̅̅̅̅̅
, pin interrupt, WDT interrupt, WKT interrupt, and
brown-out interrupt.