UM1879 Rev 4
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UM1879
Hardware layout and configuration
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Figure 8. Board jumper location
In this condition it is still possible to use the USB ST-LINK for communication, for
programming or debugging, but it is mandatory to power supply the board first using
5V_I or USB USER CN7 then connect the USB ST-LINK cable to the PC. Proceeding
this way ensures that the enumeration occurs thanks to the external power source.
The following power sequence procedure must be respected:
1.
Connect the external power source to 5V_I or USB USER CN7.
2. Power on the external power supply 5V_I or USB USER CN7.
3. Check that LD2 is turned ON.
4. Connect the PC to USB ST-LINK connector CN1.
If this order is not respected, the board may be supplied by 5V_USB_ST_LINK first
then by 5V_I or USB USER CN7 and the following risks may be encountered:
1.
If more than 300 mA current is needed by the board, the PC may be damaged or the
current supply can be limited by the PC. As a consequence the board is not powered
correctly.
2. 300 mA is requested at enumeration (since JP2 must be OFF) so there is risk that the
request is rejected and the enumeration does not succeed if the PC cannot provide
such current. Consequently the board is not power supplied (LED LD2 remains OFF).
Note:
The headers pins 5V (except in battery mode), 3V3, 2V5, 3V can be used as output power
supply when an extension board is connected to the P1 and P2 headers. The power
consumption of the extension board must be lower than 100 mA.
