C517A_99 Datasheet, PDF (199/218 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

Power Saving Modes
C517A
9 Power Saving Modes
The C517A provides three modes in which power consumption can be significantly reduced.
– Idle mode
The CPU is gated off from the oscillator. All peripherals are still provided with the clock and
are able to work.
– Power down mode
The operation of the C517A is completely stopped and the oscillator is turned off. This mode
is used to save the contents of the internal RAM with a very low standby current. Power down
mode can be entered by software or by hardware.
– Slow-down mode
The controller keeps up the full operating functionality, but its normal clock frequency is
internally divided by eight. This slows down all parts of the controller, the CPU and all
peripherals, to 1/8 th of their normal operating frequency. Slowing down the frequency greatly
reduces power consumption.
All of these modes - a detailed description of each is given in the following sections - are entered by
software. Special function register PCON (power control register) is used to select one of these
modes.
Semiconductor Group
9-1