www.ams.com/AS8650

Revision 1.1

28 - 46

AS8650B

Datasheet - Detailed Descr i p ti on

7.14 Watchdog (WD)

The WD has the following three monitory timing functions:



Start-up watchdog: Gives opportunity to microcontroller to initialize the system.



Window watchdog: Detects too early or too late microcontroller software response (loops and hangs).



Timeout watchdog: Detects too very long response from microcontroller.

7.14.1 Start-up Watchdog Behavior

Following any reset event the watchdog is used to monitor the ECU start-up procedure. Once the reset is released the watchdog counter will

start. In case the watchdog is not properly served (a trigger from microcontroller) within TWD(init), another reset is forced on RESET pin and the

monitoring procedure is restarted. The watchdog will give three opportunities to microcontroller to initialize the system. In case the watchdog is

not properly served for three times, then the system enters into Sleep mode.

7.14.2 Window Watchdog Behavior

Whenever the device enters Normal mode, the Window mode of the watchdog is activated. This ensures that the microcontroller operates within

the required speed; a too fast as well as a too slow operation will be detected. Watchdog triggering using the Window watchdog is illustrated in

Figure 12.

Figure 12. Window Watchdog Triggering

The AS8650B provides 8 different period timings. This timing can be changed through digital interface when desired. The period can be changed

The watchdog window is defined to be between 50% and 100% of the nominal programmed watchdog period. Any too early (trigger in non-

trigger window) or too late watchdog trigger will result an immediate system reset on RESET pin and watchdog entering Start-up watchdog

mode. During undervoltage condition on VLDO1 the watchdog timer is disabled.

TRIGGER WINDOW

NON-TRIGGER WINDOW

Trigger

restarts

period

50%

100%

Last

Trigger

Point

Earliest

Trigger

Point

Latest

Trigger

Point

TRIGGER WINDOW

NON-TRIGGER WINDOW

50%

100%

Earliest

Trigger

Point

Latest

Trigger

Point

Trigger restarts period

( with new period if desired)

New Period

SPI

TRIGGER

SPI

TRIGGER

Unwanted Trigger

(RESET generated,

watchdog enter Start-up

mode)