Sounds like the Xram is not working. I'm not familiar with the particular chip - do you need to set SFR registers in order to enable external data? With many of the newer chips that have internal xram, you need to write to a SFR to enable this in the startup code.

Try writing some code to write a byte to xram, and read it back and output the value out the serial port. You can use your oscilloscope to see the read/write happening and the serial ouput to check if the data is written correctly.