5.2.1 .fillupper [value] - dsPIC33C/E/F Devices Only [DD]

Define the upper byte (bits 16-23) to be used on dsPIC33C/E/F architectures when this byte is skipped due to alignment or data defining directives. If value is not specified, it is reset to the default 0x00. Directives that may cause an upper byte to be filled are: .align, .ascii, .asciz, .byte, .double, .fill, .fixed, .float, .hword, .int, .long, .skip, .space, .string and .word. The value is persistent for a given code section, throughout the entire source file, and may be changed to another value by issuing subsequent .fillupper directives.

See the Section Example - dsPIC33C/E/F Devices Only table.