NSString to NSArray

I want to split an NSString into an NSArray. For example, given开发者_JAVA百科:

NSString *myString=@"ABCDEF";

I want an NSArray like:

NSArray *myArray={A,B,C,D,E,F};

How to do this with Objective-C and Cocoa?

NSMutableArray *letterArray = [NSMutableArray array];
NSString *letters = @"ABCDEF