Hi all.
We have a bootloader in an application that requires FSxB to release to activate certain circuitry.
Just wondering if FSxB can be released when WD_WINDOW is set to 0, i.e. WD is inhibited?
Considering the datasheet which states that any WD access is considered a fault when the WD Window is closed.
Kind regards,
Joey
Thank you again for your time and reply.
Kind regards,
Joey
Hi Joey,
yes, the mechanism to clear FLT_ERR and release FS0B after multiple refreshes is expected to work when WD_WINDOW = 0. The watchdog window only affects timing constraints, not the fundamental refresh requirement.
Setting WD_WINDOW = 0 effectively disables the windowed watchdog mode, meaning the refresh is accepted at any time (classic watchdog behavior).
With Best Regards,
Jozef
Hi Jozef,
Sorry to bother you again.
Please see the following description:
This means that after power on, multiple proper refreshes are necessary to get FLT_ERR to 0 and release FS0B. I have verified this behaviour in the past.
I would like to know (because it is not explicitly stated) that this mechanism is expected to work when WD_WINDOW = 0.
Kind regards,
Joey
Thank you for your quick reply. I was actually thinking about the FLT_ERR CNT. Somehow I was under the impression that FLT_ERR starts up at 6. But I now see that this is wrong, FLT_ERR starts at 1 after POR or LPOFF.
Thank you again.
Kind regards,
Joey
Hi Joey,
Setting WD_WINDOW = 0 (0b0000) does not immediately disable the watchdog. It only becomes effective after the INIT_FS phase is closed, which requires at least one valid watchdog refresh within the 256 ms INIT_FS timeout. This applies to both FS6500 and FS4500.
After that, the watchdog is inhibited (no open/closed window enforcement), so no further WD refreshes are required.
FSxB (fail-safe outputs) are controlled by the SBC’s safety state machine. They are released when the device enters Normal mode and no fault conditions are present. Disabling the watchdog (after INIT_FS) does not prevent FSxB from being released, as long as all other safety conditions are met (e.g., no voltage faults, no overtemperature, etc.).
With Best Regards,
Jozef