C511_1 Datasheet, PDF (99/128 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

Power Saving Mode
As in normal operation mode, the ports can be used as inputs during idle mode. Thus a capture or
reload operation can be triggered, the timers can be used to count external events, and external
interrupts will be detected.
The idle mode is a useful feature which makes it possible to "freeze" the processor’s status - either
for a predefined time, or until an external event reverts the controller to normal operation, as
discussed below.
The idle mode is entered by setting the IDLE bit. Because PCON is not a bit-addressable register,
the setting of the bit has to be obtained by byte-handling instructions, e.g. by:
ORL
PCON,#00000001B ;Set IDLE bit
The instruction that sets bit IDLE is the last instruction executed before going into idle mode.
There are two ways to terminate the idle mode:
– The idle mode can be terminated by activating any enabled interrupt. This interrupt will be
serviced and the instruction to be executed following the RETI instruction will be the one
following the instruction that sets the bit IDLE.
– The other way to terminate the idle mode, is a hardware reset. Since the oscillator is still
running, the hardware reset must be held active at least for two machine cycles for a complete
reset.
Semiconductor Group
8-3