Compatibility: 3.3+
Expects: AX    6520H
DL    character to convert
                                                                  
Returns: AX    error code if CF is set to CY
DL    converted character (if no error)
                                                                  
Info: Converts the specified character to uppercase, using the
currently-active uppercase table for the active country and code
page.

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DOS Fn 6520H: Upshift Character