Mohammad,

I don't see the confusion, as I probably don't have the same doc in front of me. But this is what happens:

mem, register
00h, bank 0 R0
01h, bank 0 R1
02h, bank 0 R2
.....
07h, bank 0 R7
08h, bank 1 R0
......
0Fh, bank 1 R7
10h, bank 2 R0
....
17h, bank 2 R7
18h, bank 3 R0
....
1Fh, bank 3 R7
20h...3Fh bit addressable RAM, can also be used as normal RAM.
40h...7Fh normal RAM

The bank can be selected with 2 bank select bits. Default bank is bank 0.

I hope this clarifies your confusion a little.

Happy programming