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Monday, November 14, 2011

Power saving modes of operation of 8051

Well this mode basically includes saving energy during idle time of processor and during power down time of processor. These are utmost importance in making power saving devices.

Idle mode
  • Idle mode or sleep mode is when core of CPU is put to sleep while all on chip peripherals are on Such as timers, serial port and interrupts.
  • In this mode oscillator continues providing clock to serial port, timer, interrupt, but no clock is provided to the CPU.
  • Notice that during this mode all the register and RAM contents remain unchanged.

Power down mode
  • In power down mode the on chip oscillator is frozen which cuts of frequency to the CPU and the Peripheral functions such as timer, serial ports and interrupts.
  • This mode brings power consumption down to an absolute minimum and the contents of RAM and registers are saved and remain unchanged.


  1. will entering idle mode or power down mode stop the program execution?

    1. Yes it will. It will Halt or pause the program execution. You can co-relate this with sleep mode in a windows PC. Where the Hard Disk, CPU and other critical peripherals are turned off and whatever programs are executing will be put on hold and continue when the PC is restored.