INT 2F U - DOS 3+ internal - CHECK IF CHARACTER DEVICE
        AX = 1223h
        DS = DOS DS
        SS = DOS DS (must be using a DOS internal stack)
        SDA+218h (DOS 3.10-3.30) = eight-character blank-padded name
        SDA+22Bh (DOS 4.0-6.0) = eight-character blank-padded name
Return: CF set if no character device by that name found
        CF clear if found
            BH = low byte of device attribute word
Note:   can only be called from within DOS
SeeAlso: INT 21/AX=5D06h,INT 21/AX=5D0Bh

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