Hi Chris,

I don't use SDCC so I'm not sure how it handles and names its various memory segments, but xram sounds like external data, which is just that, external to the 89C52.

Remember that code/program memory [flash] is separate from data memory on the 8051 family uCs. The extra 128 bytes of ram in the 89C52 is addressed indirectly, and usually is called idata. See Figure 3b on your referenced document. xram should be the external data memory on the right side of the diagram.

Dennis