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Wake up from Standby mode

daweiy
Associate II
Posted on December 06, 2005 at 05:25

Wake up from Standby mode

2 REPLIES 2
daweiy
Associate II
Posted on December 06, 2005 at 03:31

Hi,

Firstly, apologies for the long post.

My question is about the Wake-Up of the STR7 after being successfully placed in Standby Mode.

Which registers are not reset on the wake up ?

The RAM loses power during standby - does any volatile memory retain stored values ?

After looking through the documentation, the following quotes seem to imply the

registers would be reset (pp 47-50 reference manual Rev7) :

''In Stop mode you stop the RCLK (core and peripherals clocks) without resetting the device,

hence preserving the MCU status......''

''When entering Standby mode the V18 domain (the kernel of the device) is powered

off while the logic belonging to the Backup block is kept powered-on. When leaving

Standby mode, all the logic belonging to the V18 domain starts from the reset state.

This means that the registers (PCU_PWRCR, RTC_ALR and RTC_PRL) that

contain bits, which affect the behaviour of Backup logic will in general not reflect its

status. These bits are in fact latched in the Backup domain to retain their value during

Standby but on leaving Standby mode, their value is not transferred back to the logic

in the V18 domain which in turn shows the reset value.''

''A wake-up event switches the power to the kernel back on. The kernel is kept under reset up

to when the internal voltage is correctly regulated....''

-----------------

The RTC is in the backup block, meaning it is kept powered on and would assume it's registers do keep their values during standby and wakeup, but this is only around 4 bytes (RTC_CNTH/L) and ideally we would be able to save up to 20 bytes - do any others retain values ?

A quick test seemed to show that R0-R12 do not retain their values, although from the following posts this would not be expected.

Index -> ARM7 STR7 -> Information needed on STANDBY mode (Posted 22-07-2005 at 18:37)

--------------------------

Posted 26-07-2005 at 14:15

.... I'm still not sure about the high-impedance thing, and whether all registers values are preserved when restarting from standby.

--------------------------

Posted 26-07-2005 at 14:32

So if I understand correctly your reply,

- All I/O pins switch to high-impedance

- **All registers values are preserved**

- Only the RAM is cleared

Right ?

--------------------------

Posted 26-07-2005 at 14:39

Hi,

Right, just All I/Os are forced to high impedance except the Standby I/Os(nSTDBY, nRSTIN, WAKEUP, RTCXTI and RTCXTO.).

--------------------------

Thanks,

Dawei

hichem2
Associate II
Posted on December 06, 2005 at 05:25

Hello dawei,

STR71x standby mode can be characterized by the following features:

- Core, memories and peripherals switched off (not powered by 1.8V internal supply) except RTC and wakeup logic.

- Main voltage regulator switched off

- All I/Os are forced to high impedance except the Standby I/Os(Standby I/Os are: nSTDBY, nRSTIN, WAKEUP, RTCXTI and RTCXTO.)

- Wake-up by: the WAKEUP pin, the RTC alarm, the LVD and RESETpin.

- MCU Reset after wake-up

By the way,after wake-up only the RTC data are preserved, concerning the reply posted it was only concerning the I/O pins states after Wake-up (Sorry for the confusion).

with best regards,

Hich :-?