N76E885 Datasheet, PDF (158/196 Pages) List of Unclassifed Manufacturers – Microcontroller

N76E885 Datasheet
23.1 Idle Mode
Idle mode suspends CPU processing by holding the Program Counter. No program code are fetched
and run in Idle mode. It forces the CPU state to be frozen. The Program Counter (PC), Stack Pointer
(SP), Program Status Word (PSW), Accumulator (ACC), and the other registers hold their contents
during Idle mode. The port pins hold the logical states they had at the time Idle was activated.
Generally, it saves considerable power of typical half of the full operating power.
Since the clock provided for peripheral function logic circuit like timer or serial port still remain in Idle
mode, the CPU can be released from the Idle mode with any of enabled interrupt sources. User can
put the device into Idle mode by writing 1 to the bit IDL (PCON.0). The instruction that sets the IDL bit
is the last instruction that will be executed before the device enters Idle mode.
The Idle mode can be terminated in two ways. First, as mentioned, any enabled interrupt will cause an
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.
23.2 Power-Down Mode
Power-down mode is the lowest power state that the N76E885 can enter. It remain the power
consumption as a ”μA” level by stopping the system clock source. Both of PU 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 N76E885 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 N76E885 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
Dec. 21, 2015
Page 158 of 196
Rev. 1.01