From the Tyros 3 reference manual, pag. 30:

● Chord Fingering Types

SINGLE FINGER Makes it simple to produce orchestrated accompaniment using major, seventh, minor and minor-seventh chords by pressing a minimum number of keys on the Chord section of the keyboard. This type is available only for Style playback.

MULTI FINGER Automatically detects Single Finger or Fingered chord fingerings, so you can use either type of fingering without having to switch fingering types.

FINGERED Lets you finger your own chords on the chord section of the keyboard, while the instrument supplies appropriately orchestrated rhythm, bass, and chord accompaniment in the selected Style. The Fingered type recognizes the various chord types which are listed on the Data List available at the Yamaha website and can be looked up using the Chord Tutor function on page 30.

FINGERED ON BASS Accepts the same fingerings as Fingered, but the lowest note played in the Chord section of the keyboard is used as the bass note, allowing you to play “on bass” chords. (In the Fingered more, the root of the chord is always used as the bass note.)

FULL KEYBOARD Detects chords in the entire key range. Chords are detected in a way similar to Fingered, even if you split the notes between your left and right hands—
for example, playing a bass note with your left hand and a chord with your right, or by playing a chord with your left hand and a melody note with your right.

AI FINGERED Basically the same as Fingered, with the exception that less than three notes can be played to indicate the chords (based on the previously played chord, etc.).

AI FULL KEYBOARD When this advanced fingering type is engaged, the instrument will automatically create appropriate ccompaniment while you play just about anything, anywhere on the keyboard using both hands. You don’t have to worry about
specifying the Style chords. Although the AI Full Keyboard type is designed to work with many songs, some arrangements may not be suitable for use with this feature. This type is similar to Full Keyboard, with the exception that less than three notes can be played to indicate the chords (based on the previously played chord, etc.). 9th, 11th and 13th chords cannot be played. This
type is available only for Style playback.

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So, to answer the question, "Full Keyboard Mode" is the way to go to play piano style on the Tyros 3, because it requires at least three notes to identify a chord.

[This message has been edited by Dreamer (edited 10-04-2008).]