Power Saving Modes
C513AO
User’s Manual
9-6
05.99
9.3
Power-down Mode
In Power-down Mode, the on-chip oscillator which operates with the XTAL pins is stopped.
Therefore, all functions of the microcontroller are stopped and only the contents of the on-chip RAM,
XRAM, and the SFRs are maintained. The port pins, which are controlled by their port latches,
output the values that are held by their SFRs. The port pins which serve the alternate output
functions show the values they had at the end of the last cycle of the instruction which initiated the
Power-down Mode. ALE and PSEN are held at logic low level (see Table 9-1).
During Power-down Mode operation,
V
DD
can be reduced to minimize power consumption. It must
be ensured, however, that
V
DD
is not reduced before Power-down Mode is invoked, and that
V
DD
is
restored to its normal operating level before Power-down Mode is terminated.
9.3.1 Invoking Power-Down Mode
Power-down Mode is entered by setting bit PDE (PCON.1). Since PCON is not a bit-addressable
register, setting the PDE bit is achieved by byte-handling instructions. For example:
ORL
PCON,#00000010B
;Set PDE bit
The instruction which sets bit PDE is the last instruction executed before going into Power-down
Mode.