DocID023833 Rev 5 11/36
STM32F42xx and STM32F43xx STM32F42xx and STM32F43xx silicon limitations
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2.1.3 Wakeup sequence from Standby mode when using more than
one wakeup source
Description
The various wakeup sources are logically OR-ed in front of the rising-edge detector which
generates the wakeup flag (WUF). The WUF needs to be cleared prior to Standby mode
entry, otherwise the MCU wakes up immediately.
If one of the configured wakeup sources is kept high during the clearing of the WUF (by
setting the CWUF bit), it may mask further wakeup events on the input of the edge detector.
As a consequence, the MCU might not be able to wake up from Standby mode.
Workaround
To avoid this problem, the following sequence should be applied before entering
Standby mode:
• Disable all used wakeup sources,
• Clear all related wakeup flags,
• Re-enable all used wakeup sources,
• Enter Standby mode
Note: Be aware that, when applying this workaround, if one of the wakeup sources is still kept
high, the MCU enters Standby mode but then it wakes up immediately generating a power
reset.
2.1.4 Full JTAG configuration without NJTRST pin cannot be used
Description
When using the JTAG debug port in debug mode, the connection with the debugger is lost if
the NJTRST pin (PB4) is used as a GPIO. Only the 4-wire JTAG port configuration is
impacted.
Workaround
Use the SWD debug port instead of the full 4-wire JTAG port.
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