SAB-C167SR-LM SIEMENS [Siemens Semiconductor Group], SAB-C167SR-LM Datasheet - Page 26

• Manufacturer Part Number: SAB-C167SR-LM
• Description: 16-Bit CMOS Single-Chip Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

C167SR
Figure 7
Block Diagram of GPT2
Watchdog Timer
The Watchdog Timer represents one of the fail-safe mechanisms which have been implemented to
prevent the controller from malfunctioning for longer periods of time.
The Watchdog Timer is always enabled after a reset of the chip, and can only be disabled in the time
interval until the EINIT (end of initialization) instruction has been executed. Thus, the chip’s start-up
procedure is always monitored. The software has to be designed to service the Watchdog Timer
before it overflows. If, due to hardware or software related failures, the software fails to do so, the
Watchdog Timer overflows and generates an internal hardware reset and pulls the RSTOUT pin low
in order to allow external hardware components to be reset.
The Watchdog Timer is a 16-bit timer, clocked with the system clock divided either by 2 or by 128.
The high byte of the Watchdog Timer register can be set to a prespecified reload value (stored in
WDTREL) in order to allow further variation of the monitored time interval. Each time it is serviced
by the application software, the high byte of the Watchdog Timer is reloaded. Thus, time intervals
between 25 s and 420 ms can be monitored (@ 20 MHz). The default Watchdog Timer interval
after reset is 6.55 ms (@ 20 MHz).
Semiconductor Group
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