topic Re: FS4500 Watchdog Disable for Reprogramming in Power Management

FS4500 Watchdog Disable for Reprogramming

GGLee — Tue, 10 Feb 2026 11:23:28 GMT

Hi NXP Team,

We are using FS4500 with TC3xx Series.

For using reprogramming, we understand that Watchdog Disable is needed.

Below is the procedure we used.

First, call FS65_RequestReset (setting RSTB_REQ of SF_OUTPUT_REQUEST).

And, send WD_WINDOW to 0000(Disable, in INIT phase only).

Finally, Watchdog Refresh within 256ms.

Question 1: Are there any additional steps required?

Question 2: There are cases where MCU reset is necessary during the reprogramming procedure. In this case, can I use those Steps again?

Regards,

GGL.

Re: FS4500 Watchdog Disable for Reprogramming

TomasVaverka — Tue, 10 Feb 2026 17:03:19 GMT

Hi Gowoon,

1. Your current sequence is correct:

Enter INIT_FS by asserting RSTB_REQ
Set WD_WINDOW = 0b0000 to disable the watchdog (valid only in INIT_FS)
Perform one correct watchdog refresh within 256ms

We also recommend disabling FCCU monitoring to prevent unintended FCCU error detection during programming. This is done by writing IO_23_FS = 0 in the INIT_FSSM register.

Once programming is complete, issue another RSTB_REQ reset so that the new software starts and the watchdog becomes active again.

2. Yes, the entire sequence can be repeated at any time.

BRs, Tomas