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XC2200 Derivatives
System Units (Vol. 1 of 2)
Startup Configuration and Bootstrap Loading
User’s Manual
10-4
V2.1, 2008-08
SCFG/BSL, V1.3
Two additional points regarding register-content after start-up must be taken into
account:
•
The register-modifications shown in
happen independently on the start-
up mode currently selected, which means also in
mode.
Next to these, in other modes -
and
(
) - more registers are additionally modified during start-
up, as described into respective Specific Settings chapters for any of the modes.
•
The values seen in some bits after start-up can be affected not only by the reset
procedure itself but also by other events during and even before the last start-up - for
example an Emergency Event can change the clock-system status.
Therefore occasional exceptions are possible from the above values (as well as from
the default register content after reset), mainly for some clock control/status flags. For
more information on such special cases and their handling - refer to XC2000
Programmer’s Guide.
10.2.2
System Frequency
The system clock which is active when the first user instruction is executed, depends on
the currently selected start-up mode and the last start-up trigger:
•
after power-on in all modes except CAN Bootstrap Loader (
) - 10MHz
(nominal value) from the XC2200 internal oscillator (doubled frequency);
•
after power-on in CAN Bootstrap Loader mode (
) - the frequency of
an external crystal connected to XTAL-pins, 4MHz minimum;
•
after any functional (not power-on) reset - the clock system configuration is not
changed by device start-up, respectively the system frequency remains as before the
reset.
10.2.3
Watchdog Timer handling
The Watchdog Timer (WDT) in XC2200 is always enabled by the start-up procedure and
configured to generate Application Reset.
Therefore, the user software must:
•
if WDT-usage is foreseen by the code - service it for a first time within approx. 65500
system clock cycles after start-up;
•
otherwise - disable it within the same time frame as above but before to execute End
of Init (EINIT).
Watchdog Timer Double Error
“Watchdog Timer Double Error” in XC2200 means the following sequence of events: