C509-L_97 SIEMENS [Siemens Semiconductor Group], C509-L_97 Datasheet - Page 219

• Manufacturer Part Number: C509-L_97
• Description: 8-Bit CMOS Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

8
The C509-L offers two on-chip peripherals which monitor the program flow and ensure an automatic
“fail-safe” reaction for cases where the controller’s hardware fails or the software hangs up:
8.1
To protect the system against software upset, the user’s program has to clear this watchdog within
a previously programmed time period. lf the software fails to do this periodical refresh of the
watchdog timer, an internal hardware reset will be initiated. The software can be designed so that
the watchdog times out if the program does not work properly. lt also times out if a software error is
based on hardware-related problems.
The watchdog timer in the C509-L is a 15-bit timer, which is incremented by a count rate of
up to
timer can be written. Figure 8-1 shows the block diagram of the watchdog timer unit.
Figure 8-1
Block Diagram of the Programmable Watchdog Timer
Semiconductor Group
– A programmable watchdog timer (WDT) with variable time-out period from 189 microseconds
– An oscillator watchdog (OWD) which monitors the on-chip oscillator and forces the
f
up to approx. 0.79 seconds at 16 MHz.
microcontroller into the reset state if the on-chip oscillator fails.
OSC
Fail Save Mechanisms
Programmable Watchdog Timer
/384. For programming of the watchdog timer overflow rate, the upper 7 bit of the watchdog
8-1
Fail Save Mechanisms
1997-10-01
C509-L
f
OSC
/12