OPTIREG™ SBC TLE9274QXV33
Supervision functions
In case of a watchdog reset, SBC Restart mode is started and the SPI bits WD_FAIL are set. Once the RO goes
HIGH again the watchdog immediately starts with a long open window and the SBC enters automatically
SBC Normal mode.
In SBC Development mode, no reset is generated due to a watchdog failure, the watchdog is OFF.
After 3 consecutive resets due to watchdog failures, additional resets can be prevented by setting the
MAX_3_RST bit on WD_CTRL register. The SBC will then remain in SBC Normal or Stop mode (the device will
not reenter SBC Restart mode).
13.2.1
Time-out watchdog
The time-out watchdog is an easier and less secure watchdog than a window watchdog as the watchdog
trigger can be done at any time within the configured watchdog timer period.
A correct watchdog service immediately results in starting a new watchdog timer period. Taking the
tolerances of the internal oscillator into account leads to the safe trigger area as defined in Figure 39.
If the time-out watchdog period elapses, a watchdog reset is created by setting the reset output RO low and
the SBC switches to SBC Restart mode.
Typical timout watchdog trigger period
tWD x 1.50
open window
uncertainty
Watchdog Timer Period (WD_TIMER)
tWD x 1.20
tWD x 1.80
t / [tWD_TIMER
]
safe trigger area
Figure 39 Time-out watchdog definitions
13.2.2
Window watchdog
Compared to the time-out watchdog, the characteristic of the window watchdog is that the watchdog timer
period is divided between a closed and an open window. The watchdog must be triggered inside the open
window.
A correct watchdog trigger results in starting the window watchdog period by a closed window followed by an
open window.
The watchdog timer period is at the same time the typical trigger time and defines the middle of the open
window.
Taking the oscillator tolerances into account leads to a safe trigger area of:
tWD × 0.72 < safe trigger area < tWD × 1.20
The typical closed window is defined to a width of 60% of the selected window watchdog timer period. Taking
the tolerances of the internal oscillator into account leads to the timings as defined in Figure 40.
A correct watchdog service immediately results in starting the next closed window.
Datasheet
86
Rev.2.0
2022-05-06
INFINEON [ Infineon ]
