The Z8000 as supports both members of the Z8000 family: the unsegmented Z8002, with 16 bit addresses, and the segmented Z8001 with 24 bit addresses.
When the assembler is in unsegmented mode (specified with the
unsegm directive), an address takes up one word (16 bit)
sized register. When the assembler is in segmented mode (specified with
the segm directive), a 24-bit address takes up a long (32 bit)
register. See Assembler Directives for the Z8000,
for a list of other Z8000 specific assembler directives.