Posted on December 06, 2005 at 03:31Hi,
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....''
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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)
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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.
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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 ?
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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.).
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Thanks,
Dawei
