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The first firmware application contains the USB Library, the DFU layer and the HDFlash driver.

This firmware application must be placed in Sector 0. It is executed only when the USB cable

is plugged-in. This firmware cannot be modified during the DFU process. When the Flash up-

grade is finished, the firmware in Sector 0 continues execution until the USB cable is removed.

The second firmware application is the main application. It must be placed in Sectors 1 or 2

because it is modified during the DFU process. This firmware is executed only when the USB

cable is not plugged into the board.

The DFU layer also allows you to upgrade only one sector. You can use this feature, for ex-

ample, to store common data or code for any firmware loaded in Sector 2.

2.2 USB CABLE DETECTION

The detection of the USB cable is made through an I/O port configured in Input mode. This

I/O is connected to the Vbus line on the USB connector. Detection can be done with interrupts

or by polling. In our example, the polling method is used. This detection must be performed by

both applications (main application and DFU).

Figure 2. Connecting an I/O Port to the Vbus line

+5V

USB connector

Vbus

USB Vcc

Vdd

Vss

I/O