C504 Datasheet, PDF (33/49 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

C504
Power Saving Modes
Two power down modes are available, the idle mode and power down mode.
– In the idle mode the oscillator of the C504 continues to run, but the CPU is gated off from the
clock signal. However, the interrupt system, the serial port, the A/D converter, 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.
– In the power down mode, the RC oscillator and 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 SFR's are maintained. The port pins, which are
controlled by their port latches, output the values that are held by their SFR's.
Table 10 gives a general overview of the power saving modes.
Table 10
Power Saving Modes Overview
Mode
Idle mode
Power-Down
Mode
Entering
2-Instruction
Example
ORL PCON, #01H
ORL PCON, #20H
ORL PCON, #02H
ORL PCON, #40H
Leaving by
Remarks
Ocurrence of an
interrupt from a
peripheral unit
Hardware Reset
CPU clock is stopped;
CPU maintains their data;
peripheral units are active (if
enabled) and provided with
clock
Hardware Reset
Oscillator is stopped;
Wake-up from power ^{contents of on-chip RAM and}
down
SFR’s are maintained;
In the power down mode of operation, V_CC can be reduced to minimize power consumption. It must
be ensured, however, that V_CC is not reduced before the power down mode is invoked, and that V_CC
is restored to its normal operating level, before the power down mode is terminated.
The idle mode can be terminated by activating any enabled peripheral interrupt or by resetting the
C504. The power down mode can be terminated using an interrupt by a short low pulse at the pin
P3.2/AN4/INT0 or by resetting the C504. If a power saving mode is left through an interrupt, the
microcontroller state (CPU, ports, peripherals) remains preserved. If a power saving mode is left by
a reset operation, the microcontroller state is disturbed and replaced by the reset state of the C504.
Semiconductor Group
33