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XC2200 Derivatives
System Units (Vol. 1 of 2)
Startup Configuration and Bootstrap Loading
User’s Manual
10-5
V2.1, 2008-08
SCFG/BSL, V1.3
1. WDT overflow happens - WDT rolls from FFFF
H
to 0000
H
and enters Prewarning
Mode;
2. device starts-up anew - could be due to WDT-reset (unavoidable once Prewarning
Mode is entered) or another reset request triggered before Prewarning Mode been
expired;
3. a following WDT-reset causes the next - after the start-up according to
- device
restart.
In other words, in this scenario WDT overflow happens two times one after another with
one device restart in between.
Such a situation is considered as indicating major and systematic malfunction and the
device enters
).
This (WDT Double Error) feature is supported in XC2200 by
bit in
register (refer to
) which bit is copied by the start-up procedure from
WDT Control and Status Register
SCU_WDTCS.OE is reset immediately afterwards. Next, upon any device restart the
following conditions are checked by the start-up procedure:
•
•
Is the start-up caused by a WDT-reset?
If both the above conditions are true - a Watchdog Timer Double Error is recognized and
is immediately entered by the device.
Therefore, if entering power-save mode upon WDT Double Error is not desired for some
reasons, the user software must care to reset
bit. Different
possibilities for handling exist:
•
reset the bit always at the beginning of application code or inside the WDT
Prewarning Mode handler routine (if any) - in such a case WDT Double Error will be
never recognized;
•
reset the bit together with servicing the WDT - in such a case WDT Double Error will
be recognized only if WDT has not been serviced at all after the previous overflow
and device restart.
Note: If after the first WDT overflow/device restart a second reset is triggered by another
source but not WDT, the
bit will be automatically reset by
the start-up procedure.
10.2.4
Start-up Error state
To prevent possible negative consequences for the device and/or the system, upon
unrecoverable error during startup XC2200 is put onto a stable, passive and neutral to
the external world state - power-save mode with DMP_1 shut down and DMP_M
powered with 1V.
This state can be exited with power-on reset only.