C509-L_97 Datasheet, PDF (229/290 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

Power Saving Modes
C509-L
9.3 Idle Mode
In idle mode the oscillator of the C509-L continues to run, but the CPU is gated off from the clock
signal. However, the interrupt system, the serial channels, the A/D converter, the oscillator
watchdog, the division/multiplication unit and all timers, except for the watchdog timer, are further
provided with the clock. The CPU status is preserved in its entirety: the stack pointer, program
counter, program status word, accumulator, and all other registers maintain their data during idle
mode.
The reduction of power consumption, which can be achieved by this feature, depends on the
number of peripherals running. lf all timers are stopped and the A/D converter and the division/
multiplication unit are not running, maximum power reduction can be achieved. This state is also the
test condition for the idle I_CC in the DC characteristics.
Thus, the user has to take into account that the right peripheral continues to run or is stopped,
respectively, during idle. Also, the state of all port pins - either the pins controlled by their latches or
controlled by their secondary functions - depends on the status of the controller when entering idle.
Normally the port pins hold the logical state they had at the time idle was activated. lf some pins are
programmed to serve their alternate functions they still continue to output during idle if the assigned
function is on. This applies for the compare outputs as well as for the system clock output signal and
the serial interface in case the latter could not finish reception or transmission during normal
operation. The control signals ALE and PSEN are held at logic high levels (see table 9-1).
During idle, as in normal operating mode, the ports can be used as inputs. Thus, a capture or reload
operation as well as an A/D conversion can be triggered, the timers can be used to count external
events and external interrupts can be detected.
Semiconductor Group
9-4
1997-10-01