srinivas,

I hope it's clear that either decode allows full access to the 128 ram memory.

Felix's decode alternates between selecting I/O or RAM in the Data Memory Map. When the RAM is in place you select, using A16, which 64K page is in place.

The other decode allows the I/O to exist in the lower 32K of data memory concurent with what ever 32K page you select using MA15,MA16 in the upper 32K of data memory.

regards,
p