The Triscend has up to 32 external address lines - so you can have up to 4GB of Flash, if you really want!!!

The mapping from this to the 8051's 16-bit address space is all simply configurable at runtime by use of the Mapper registers - no special hardware required!

However, rather than code banking - which is nasty, you might like to look at Keil's facility to place constants (including strings) into the XDATA address space. This frees up CODE address space, without having to resort to the overheads & difficulties of code banking. With the Triscend Mappers, it's a doddle!

http://www.keil.com/discuss/docs/thread3644.htm