AN4253 datasheet(18/44 Pages) STMICROELECTRONICS

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Safe mode block

AN4253

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DocID024255 Rev 2

Safe mode block

Figure 8. Flow of the "Safe mode handling" phase

Safe mode is a special mode of the microcontroller where only limited part of the hardware

functionality is enabled to the user. All attempts to change the HW configuration are blocked

until fault conditions are removed.

Very often safe mode is observed in the startup phase after a functional reset other then

functional reset initiated from software. In such situation startup has to leave safe mode

prior to any mode change transition.

Conditions to leave safe mode are:

•

No FCCU fault pending

•

FCCU flags in RGM.FES register cleared

6.1

Read current mode of the microcontroller

Current mode of the microcontroller is reported in Mode Entry Global Status (ME.GS)

6.1.1

Code sequence

32 bit read of ME.GS register (0xC3FDC000)

6.2

Safe mode check

It is needed to extract S_CURRENT_MODE bit field from the read value. There are only two

possible values after the reset:

•

2 = SAFE

•

3 = DRUN

AN4253 Datasheet(PDF) 18 Page - STMicroelectronics