STR91XF datasheet(17/72 Pages) STMICROELECTRONICS

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STR91xF

Functional overview

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The STR91xF supports the following three global power control modes:

●

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 optional RTC clock. Wake up unit remains powered,

PLL is forced off.

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.

2.11.1 Run 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.

2.11.2 Idle mode

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:

●

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 (optionally does not cause interrupt)

Note:

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.

2.11.3 Sleep mode

In this mode all clock circuits except the RTC are turned off and main oscillator input pins

X1_CPU and X2_CPU are disabled. The entire chip is quiescent (except for RTC and wake-up

circuitry). There are three means to exit Sleep Mode and re-start the system:

●

Some resets (external reset pin, low-voltage, power-up, JTAG debug command)

●

RTC alarm

●

Input from wake-up unit

2.12

Voltage supplies

The STR91xF requires two separate operating voltage supplies. The CPU and memories

operate from a 1.65V to 2.0V on the VDD pins, and the I/O ring operates at 2.7V to 3.6V on the

VDDQ pins.

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