Well the hitachi white papers say 5v but 3.3 for the later versions used in handhelds etc. Feel free to prove me wrong.
I trust the product code, I just would have thought otherwise for the time. A 5V CPU would make it probably the last 5V friendly console. As everything was certainly CMOS, they really should have gone with 3.3V. Now unless the output level is actually 3.3V (probably indicated in the datasheet), you'll have problems interfacing with today's very un-5V-friendly devices.
I'll probably come across my documentation in a couple of weeks as I'm having a big sort-out. If I don't remember, give me a shout if you still need to know.
