AN3316 datasheet(23/42 Pages) STMICROELECTRONICS

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AN3316

Device modes

Doc ID 18232 Rev 2

23/42

Request transition to RUN0 mode:

The transition from a mode to another is handled by software by accessing the mode

control ME_MCTL register twice by writing:

–

the first time with the value of the key (0x5AF0) into the KEY bit field and the

required target mode into the TARGET_MODE bit field

–

the second time with the inverted value of the key (0xA50F) into the KEY bit field

and the required target mode into the TARGET_MODE bit field.

So, in case of DRUN

RUN0 transition, these two register writing should be done:

ME.MCTL.R = 0x40005AF0

ME.MCTL.R = 0x4000A50F

DRUN

RUN0 mode:

Once a valid mode transition request is detected, the transition starts. Here, device

switches-on/off modules and peripherals without CPU intervention.

It is possible to check for transition completion through mode Transition Status bit:

While (ME.GS.MTRANS != 0)

//transition ongoing

... //transition completed

...

In ordeI to prevent code stucking waiting for transition completion, it could be better to

check transition timing through a timer. Timer timeout calculation should be based on

modules/peripherals start-up timing. In this case this value is close to XTAL start-up

time (at maximum 6 msec).

RUN0 mode:

Otherwise, if transition completion is signaled by sw, the RUN0 is properly entered with

the modules configured as expected.

Scenario 2 (RUN0  HALT  RUN0)

This scenario deals with HALT mode that is the only one allowing to reduce average

consumption while the application is 100% functional. In fact, reducing dynamic

consumption through core switching-off and togheter with maintaining the full functionality is

one of the new challenge in body.

Figure 12.

Scenario 2 - finite state machine

Hardware triggered transition

Software triggered transition

RUN0

HALT

XTAL, PLL = ON

sysclk = PLL-64MHz

CFLASH = ON

DFLASH = Low Power

SPI0, ADC0 = ON

XTAL, PLL = ON

sysclk = PLL-64MHz

CFLASH = Low Power

DFLASH = Low Power

SPI0, ADC0 = ON

CAN0 = ON

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