Has anyone ever discovered this before? Has this ever been discussed here? I know there have been discussions on other parts of the forum about what a slash chord is and how to get the auto-accompaniment to play them on the higher-end keyboards, but I don't remember seeing anything about them discussed for the PSR-E series keyboards, and I never thought that these keyboards were capable of them, but they are! I generally do not use auto-accompaniment, but I just discovered this accidentally on my PSR-E433 while researching an answer to another question related to single finger chords on an E463 in another part of the forum.
A "slash chord" is simply a chord that is denoted by the chord symbol, followed by the slash, followed by the note that is supposed to be played on the bass. So for example, if you are looking at a piece of sheet music and see the chord symbol "C", that tells you to play a C major chord, and that the bass note should also be C, as there is nothing to say otherwise about the bass note. But if you see the chord symbol "C/G", that tells you to play a C major chord, but for the bass note to be a G.
Normally, what I've seen is that on the PSR-E series, if you play the full, complete chord while in auto-accompaniment mode, you'll always get the root bass, no matter what inversion you play the chord. So, if you play C,E,G, or E,G,C, or G,C,E, you'll always get a C major chord with a C bass. But what I discovered is that there are certain 2-note combinations that can trigger a slash chord on the PSR-E series -- or at least on my E433. When I play a C and the G a fourth below the C together, I get a C major accompaniment, but with the bass note being G. If I play a C and an E a minor 6th below the C together, I get a C major accompaniment, but with the bass note being an E. Seems to work for minor chords, as well, at least in some cases, as playing C and Eb a major 6th below the C -- I believe -- got me a C-minor chord with an Eb bass. I haven't tried other combinations. And I'm sure that more intricate slash chords, such as C with B for the bass, may not be possible, because the keyboard might recognize those notes in a different fashion (I think if you play a C and the B right below it together, you'll be in easy-play mode and get a C7).
Like I said, I don't ever remember seeing this discussed before. Certainly feel free to post if you know of other note combinations that trigger non-root bass notes, and let me know if anything I posted above is incorrect.