MLX75030 Datasheet, PDF (57/72 Pages) Melexis Microelectronic Systems – Universal ActiveLight Sensor Interface

MLX75030 Universal ActiveLight Sensor Interface
Datasheet
7.5. Window Watchdog Timer
The internal watchdog timer is a watchdog based on two different windows: an open and a closed window. During the open
window the master can restart the watchdog timer. During the closed window, no restarts are accepted.
The restart (re-initialisation) of the watchdog timer happens via the WT (Watchdog Trigger) pin: when a falling edge is
detected on the WT pin, the watchdog will be restarted.
The low time on the WT pin should be at least a time t_{wt_l}.
After a POR or a reset issued by the watchdog and after a wake-up from Sleep Mode (either by uploading the NRM
command, or by using the WAKE_UP pin), the window watchdog will open an active window of a time t_{wdt_init}, during which a
watchdog restart must be issued by the µC. If no watchdog restart is received by the end of the open window, the µC will be
reset.
After this initial period, the window watchdog is programmed to wait a time t_{wdt_closed} during which no watchdog restarts are
allowed. If a watchdog restart is sent during the closed window time, the watchdog will reset the master via the MR (Master
Reset) pin.
After a closed window, an open window of a time t_{wdt_open} will follow during which a watchdog restart is expected. If no
watchdog restart is received till the end of the open window, the µC will be reset via the MR pin.
Changing mode between Normal Running Mode and Standby Mode will not influence the watchdog timing or state. Also a
CR command will not change the used window times. The watchdog counter will not be influenced when changing mode
between NRM and STBY or when uploading a CR command.
The Watch Dog Timer is disabled in Sleep Mode. A falling edge on the WT pin in the Sleep Mode will set an error flag in the
register ‘Err’. Coming back from Sleep Mode to Normal Running Mode always restarts the watchdog with the initial timing
window.
This figure shows what timing windows are used in the different operating modes:
POR
Device State
NRM
WDT Window
t_{wdt_init}
STBY
NRM
SLP
NRM
t_{wdt_init}
Figure 16 : Window times during different operating modes
The two diagrams below show the functionality of the watchdog timer:
REVISION 005 – DECEMBER 2013
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