Ah right, non-tile based then I guess. I tried all the usual tile combinations and didn't find anything. That definitely rules out it being a NES-VT clone as RB speculated it might be, that's all strictly tile-based stuff.
Still the way the CPU runs is odd, so it's still possible there's an internal bootstrap of some kind, because there really are no boot vectors that a 6502 would need for booting / interrupts..
It's an odd one, we do know that 6502s did end up being heavily customized by this point, and we've even seen systems with brand new opcodes that aren't even part of the usual 6502 set, so working out what is actually going on could be tricky.
