ATMEL 89C51 HAVE TWO POWER SAVING MODE WITH DIAGRAM
1.IDLE MODE
2.POWER DOWN MODE
IDLE mode:
the AT89C51 goes into idle mode as soon as it execute a instruction that set PCON.0=1.
idle mode also called sleep mode.in this mode the internal clock is not given to CPU.but interrupt,timer and ,serial port function continue normal.the SP,PC,PSW, accumulator and other register maintain there data during idle mode.
ALE and PSEN held high in this mode.
in idle mode , the CPU puts itself to sleep while all the on chip peripherals remain active.
the mode is invoked by software.the content of the on chip RAM and all the special function register remain unchanged during this mode.the idle mode.the idle mode can be terminated by any enable interrupt or by hardware reset.
there are two way to terminate the idle mode.activation of any interrupt will goes PCON.0 to be clear.thus the idle mode will terminate.
PCON is a register . it is a 8 bit register. there bit are PCON.7 MSB bit
to PCON.0 LSB bit(we can see it right side)
interrupt will service and following RST instruction,the next instruction to be executed that put the device idle.
for example.. if MOV A,FFFFH instruction .during this execution the micro controller go to idle mode.after the termination of idle mode.this execution started and continue the execution cycle.
other way of terminating the idle mode by using the hardware interrupt.the device normally resumes program execution ,from where it left off,up to two machine cycle before the internal reset algorithm take control.on chip hardware inhibits access to internal RAM in this event,but access to the port pin is not inhibited.To eliminated the possibility of an unexpected wriet to a port pin when idle is terminated by reset,the instruction following the one that invokes idle should not be one that write to port pin or to external memory.
POWER DOWN MODE
POWER DOWN MODE is activated by executing an instruction that set PCON.1.in power down mode the on chip oscillator is stop .with clock not available.all functions are stop.the content of the onchip RAM and special function register are maintain.
ALE and PSEN are held low.the only exit from power down mode is hardware reset.
power down mode VCC can be reduced as low as 2 v however VCC should not redused before the power down mode is activated.and VCC is restored it's normal level before the power down mode is terminated.
PCON REGISTER
....................................................................................................PCON.1...... PCON.0
Labels: ATMEL 89C51
