Addressing External Memory

Hello,

BASE_ADDR = 0x8000
i=1

A)may I know what is
#define COMMAND(i) (*((volatile char xdata *)(BASE_ADDR +i)))

B)Is is better to address the "command register" of an external chip as XDATA of 8051 chip(using ALE,Port0,Port2,etc) or should I just manually arrange some I/O pins (of 8051) to do that?

Regards,
KC

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