ST STM32F205 series Reference Manual page 170

Interrupts and events
generated. The pending bit corresponding to the interrupt line is also set. This request is
reset by writing a '1' in the pending register.
To generate the event, the event line should be configured and enabled. This is done by
programming the two trigger registers with the desired edge detection and by enabling the
event request by writing a '1' to the corresponding bit in the event mask register. When the
selected edge occurs on the event line, an event pulse is generated. The pending bit
corresponding to the event line is not set.
An interrupt/event request can also be generated by software by writing a '1' in the software
interrupt/event register.
Hardware interrupt selection
To configure the 23 lines as interrupt sources, use the following procedure:
• Configure the mask bits of the 23 interrupt lines (EXTI_IMR)
•
Configure the Trigger selection bits of the interrupt lines (EXTI_RTSR and EXTI_FTSR)
• Configure the enable and mask bits that control the NVIC IRQ channel mapped to the
external interrupt controller (EXTI) so that an interrupt coming from one of the 23 lines
can be correctly acknowledged.
Hardware event selection
To configure the 23 lines as event sources, use the following procedure:
• Configure the mask bits of the 23 event lines (EXTI_EMR)
•
Configure the Trigger selection bits of the event lines (EXTI_RTSR and EXTI_FTSR)
Software interrupt/event selection
The 23 lines can be configured as software interrupt/event lines. The following is the
procedure to generate a software interrupt.
•
Configure the mask bits of the 23 interrupt/event lines (EXTI_IMR, EXTI_EMR)
•
Set the required bit in the software interrupt register (EXTI_SWIER)
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