C508_01 Datasheet, PDF (239/267 Pages) Infineon Technologies AG – 8-Bit CMOS Microcontroller

C508
Power Saving Modes
9.2
Idle Mode
In the idle mode, the oscillator of the C508 continues to run, but the CPU is gated off from
the clock signal. However, the interrupt system, the serial port, the A/D Converter, the
Capture/Compare Unit, and all timers (with the exception of 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. If all timers are stopped, and the A/D Converter
and the serial interfaces are not running, the maximum power reduction can be
achieved. This state is also the test condition for the idle mode I_DD.
Thus, the user must be cautious in determining which peripheral should continue to run
and which must be stopped during idle mode. 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 mode.
Normally, the port pins hold the logical state they had at the time that the idle mode was
activated. If some pins are programmed to serve as alternative functions, they still
continue to output during idle mode if the assigned function is on. This especially applies
to the serial interface in case it cannot finish reception or transmission during normal
operation. The control signals ALE and PSEN are held at logic high levels.
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 Watchdog Timer is the only peripheral which
is automatically stopped during idle mode.
User’s Manual
9-3
2001-05