str912fa STMicroelectronics, str912fa Datasheet - Page 17

• Manufacturer Part Number: str912fa
• Description: Arm966e-s? 16/32-bit Flash Mcu With Ethernet, Usb, Can, Ac Motor Control, 4 Timers, Adc, Rtc, Dma
• Manufacturer: STMicroelectronics

STR91xFA
2.11
2.11.1 Run mode
2.11.2 Idle mode
Note:
at 48 MHz, and the Ethernet interface at 25 MHz. The RTC is always running in the background
at 32.768 kHz, and the CPU can go to very low power mode dynamically by running from
32.768 kHz and shutting off peripheral clocks and the PLL as needed.
Flexible power management
The STR91xFA offers configurable and flexible power management control that allows the user
to choose the best power option to fit the application. Power consumption can be dynamically
managed by firmware and hardware to match the system’s requirements. Power management
is provided via clock control to the CPU and individual peripherals.
Clocks to the CPU and peripherals can be individually divided and gated off as needed. In
addition to individual clock divisors, the CCU master clock source going to the CPU, AHB, APB,
EMI, and FMI can be divided dynamically by as much as 1024 for low power operation.
Additionally, the CCU may switch its input to the 32.768 kHz RTC clock at any time for low
power.
The STR91xFA supports the following three global power control modes:
●
●
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A special mode is used when JTAG debug is active which never gates off any clocks even if the
CPU enters Idle or Sleep mode.
This is the default mode after any reset occurs. Firmware can gate off or scale any individual
clock. Also available is a special Interrupt Mode which allows the CPU to automatically run full
speed during an interrupt service and return back to the selected CPU clock divisor rate when
the interrupt has been serviced. The advantage here is that the CPU can run at a very low
frequency to conserve power until a periodic wake-up event or an asynchronous interrupt
occurs at which time the CPU runs full speed immediately.
In this mode the CPU suspends code execution and the CPU and FMI clocks are turned off
immediately after firmware sets the Idle Bit. Various peripherals continue to run based on the
settings of the mask registers that exist just prior to entering Idle Mode. There are 3 ways to exit
Idle Mode and return to Run Mode:
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●
●
It is possible to remain in Idle Mode for the majority of the time and the RTC can be
programmed to periodically wake up to perform a brief task or check status.
Run Mode: All clocks are on with option to gate individual clocks off via clock mask
registers.
Idle Mode: CPU and FMI clocks are off until an interrupt, reset, or wake-up occurs. Pre-
configured clock mask registers selectively allow individual peripheral clocks to continue
run during Idle Mode.
Sleep Mode: All clocks off except RTC clock. Wake up unit remains powered, PLL is
forced off.
Any reset (external reset pin, watchdog, low-voltage, power-up, JTAG debug command)
Any interrupt (external, internal peripheral, RTC alarm or interval)
Input from wake-up unit on GPIO pins
Functional overview
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