C515C_9711 Datasheet, PDF (230/268 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

Power Saving Modes
C515C
9.8 CPUR Signal
The dedicated output pin CPUR of the C515C provides a control output signal, which indicates
when the CPU is running and executing instructions from internal ROM or external program
memory. In this state CPUR is set to low level. CPUR is inactive (floating or set to high level) in the
following states of the CPU :
– in hardware power down mode
– in software power down mode
– in idle mode
– with an active RESET input signal
In a microcontroller application with the C515C, CPUR typically can be used to put an external
program memory device (EPROM) into its power saving mode (chip enable = high) when the
C515C is put into power down mode or idle mode.
The timing diagram in figure 9-5 shows the typical behaviour of the CPUR signal when entering
and leaving the software power down mode.
ALE
PSEN
CPUR
Last instruction fetches
before entering software
power down mode
Software power down
mode active
First instruction fetches
of normal mode
(e.g. interrupt entry)
MCT02760
Figure 9-5
CPUR Timing in Software Power Down Mode
Note: In hardware power down mode, CPUR is at floating level. In software power down mode, idle
mode, and with an active RESET input signal CPUR is set to high level.
Semiconductor Group
9-15
1997-11-01