Or you could use a regex with zero-lookahead-pattern:

my $line = q(!A001ST!,!AD,CD!,!1!,!20/05/2004!,!ANDORRA!,!0!,!EUR,USD!
+,!6!,!7!,!0!,!AD!,!1!);

# only commas followed by "!" split fields
my @data = split(/\,\s*(?=!)/, $line);
print "Data splitted is as below \n";
print join("==>",@data),"\n";
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From perldoc perlre:

"(?=pattern)"
                 A zero-width positive look-ahead assertion.  For
                 example, "/\w+(?=\t)/" matches a word followed
                 by a tab, without including the tab in $&.
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