STM32F412RGH3TR datasheet(23/201 Pages) STMICROELECTRONICS

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STM32F412xE/G

Functional overview

3.13

Nested vectored interrupt controller (NVIC)

The devices embed a nested vectored interrupt controller able to manage 16 priority levels,

and handle up to 81 maskable interrupt channels plus the 16 interrupt lines of the

Cortex®-M4 with FPU.

•

Closely coupled NVIC gives low-latency interrupt processing

•

Interrupt entry vector table address passed directly to the core

•

Allows early processing of interrupts

•

Processing of late arriving, higher-priority interrupts

•

Support tail chaining

•

Processor state automatically saved

•

Interrupt entry restored on interrupt exit with no instruction overhead

This hardware block provides flexible interrupt management features with minimum interrupt

latency.

3.14

External interrupt/event controller (EXTI)

The external interrupt/event controller consists of 21 edge-detector lines used to generate

interrupt/event requests. Each line can be independently configured to select the trigger

event (rising edge, falling edge, both) and can be masked independently. A pending register

maintains the status of the interrupt requests. The EXTI can detect an external line with a

pulse width shorter than the Internal APB2 clock period. Up to 114 GPIOs can be connected

to the 16 external interrupt lines.

3.15

Clocks and startup

On reset the 16 MHz internal RC oscillator is selected as the default CPU clock. The

16 MHz internal RC oscillator is factory-trimmed to offer 1% accuracy at 25 °C. The

application can then select as system clock either the RC oscillator or an external 4-26 MHz

clock source. This clock can be monitored for failure. If a failure is detected, the system

automatically switches back to the internal RC oscillator and a software interrupt is

generated (if enabled). This clock source is input to a PLL thus allowing to increase the

frequency up to 100 MHz. Similarly, full interrupt management of the PLL clock entry is

available when necessary (for example if an indirectly used external oscillator fails).

Several prescalers allow the configuration of the three AHB buses, the high-speed APB

(APB2) and the low-speed APB (APB1) domains. The maximum frequency of the three AHB

buses and high-speed APB domains is 100 MHz. The maximum allowed frequency of the

low-speed APB domain is 50 MHz.

The devices embed a dedicated PLL (PLLI2S) which allows to achieve audio class

performance. In this case, the I2S master clock can generate all standard sampling

frequencies from 8 kHz to 192 kHz.

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