data memory

hello,

I am using BL4S200 for my project. I need memory for Modbus address. I try to use xalloc  or _xalloc to distribute the memory for this usage. I roughly need 6k byte for modbus address. so however, I will use logic memory address for modbus address, so I need a mapping logic between modbus address and physical address. But I can't assign a physical start address when I use xalloc, does anybody know how to do it, or other some method for this feature?