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2 DFU MECHANISM

2.1 OVERVIEW

As mentioned in the introduction, the microcontroller’s USB cell is only used during the DFU

upgrade process. This upgrade process takes place only when the USB cable is plugged-in.

When the USB cable is removed the non-USB application is executed and the USB cell is

switched off. The following figure explains this mechanism in detail.

Figure 1. DFU Flowchart in a non-USB application

As you can see, two separate firmware applications reside in different flash sectors and are

selected by plugging a cable in the USB connector.

USB cable ?

DFU Process

Main (Application)

Main (DFU)

MCU Reset

Yes

SECTOR 0

SECTORS 1 & 2

USB cable ?

No

Yes

No

WDG Reset

Flash

erasing &

programming

(jump table)

USB cable ?

WDG Reset

No

Yes

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