Support 16 bit color on QNX 6.2 / XScale ?

I’m using QNX 6.2.0 on Intel daytona (XScale) board.
On this system, io-graphics is exeucted with 8bit color mode like below as

io-graphics -g640x350x8 -a mode=/proc/boot/pxa250.conf

As far as I know, daytona board supports 16bit mode. So I just changed above
parameters to like below.

io-graphics -g640x350x16 -a mode=/proc/boot/pxa250.conf

But screen doesn’t appear, just black screen.
What should I do for running Photon with 16bit mode on Intel Daytona Board ?