SAB80C515A-5 SIEMENS [Siemens Semiconductor Group], SAB80C515A-5 Datasheet - Page 32

• Manufacturer Part Number: SAB80C515A-5
• Description: 8-Bit CMOS Single-Chip Microcontroller Family
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

After the on-chip oscillator finally has started, the oscillator watchdog detects the correct function;
then the watchdog still holds the reset active for a time period of 768 cycles of the RC oscillator in
order to allow the oscillation of the on-chip oscillator to stabilize (figure 4-4, II). Subsequently the
clock is supplied by the on-chip oscillator and the oscillator watchdog’s reset request is released
(figure 4-4, III). However, an externally applied reset still remains active (figure 4-4, IV) and the
device does not start program execution (figure 4-4, V) before the external reset is also released.
Although the oscillator watchdog provides a fast internal reset it is additionally necessary to apply
the external reset signal when powering up. The reasons are as follows:
The external reset signal must be hold active at least until the on-chip oscillator has started and the
internal watchdog reset phase is completed. An external reset time of more than 50 s should be
sufficient in typical applications. If only a capacitor at pin Reset is used a value of less than 100 nF
provides the desired reset time.
Semiconductor Group
– Termination of Hardware Power Down Mode (a HWPD signal is overridden by reset)
– Termination of Software Power Down Mode
– Reset of the status flag OWDS that is set by the oscillator watchdog during the power up
sequence.
4-9
System Reset