Programming the Flash Configuration Field (FCF) at firmware

wane — Thu, 16 Apr 2026 12:29:10 GMT

Hello,

I'm examining the best way to turn on secure the debugger port at firmware level.
As you know, default value of values of the backdoor key and other configuration field as follows.
0x400..0x407: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
0x408..0x40F: 0xFF 0xFF 0xFF 0xFF 0xFE 0xFF 0xFF 0xFF

For change FCF values, can I program the FCF value without sector erase?
Because all bits have 1's excepting FSEC|SEC data, I have tried this way with successful.
Is this way can make a ECC problem (bricking)?
Or sector erase step must be done before programming?
Is there any other way of program FCF to recommend?

Regards,

Re: Programming the Flash Configuration Field (FCF) at firmware

Senlent — Fri, 17 Apr 2026 10:24:28 GMT

Hi@wane

1. The FCF configuration can be modified in the startup file, so users don't need to use FTFC instructions to erase and rewrite the FLASH in the code.

2. If you want to modify the FCF in the application code, it's recommended that you erase it first. Secondary modifications to the FCF may pose risks, such as the ECC error you mentioned.

topic Programming the Flash Configuration Field (FCF) at firmware in S32K

Programming the Flash Configuration Field (FCF) at firmware

Re: Programming the Flash Configuration Field (FCF) at firmware