Datasheet

Functional overview STM32F401xD STM32F401xE
18/135 DocID025644 Rev 3
3.9 Nested vectored interrupt controller (NVIC)
The devices embed a nested vectored interrupt controller able to manage 16 priority levels,
and handle up to 62 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.
3.10 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 81 GPIOs can be connected
to the 16 external interrupt lines.
3.11 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 84 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 two AHB buses, the high-speed APB
(APB2) and the low-speed APB (APB1) domains. The maximum frequency of the two AHB
buses is 84 MHz while the maximum frequency of the high-speed APB domains is 84 MHz.
The maximum allowed frequency of the low-speed APB domain is 42 MHz.
The devices embed a dedicated PLL (PLLI2S) which allows to achieve audio class
performance. In this case, the I
2
S master clock can generate all standard sampling
frequencies from 8 kHz to 192 kHz.
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