ADDRESS_SPACE definition are a variable number of sub-block definitions called BusBlocks, as shown in the following example:
Each Bus Block contains block RAM Bit Lane definitions that are accessed by a parallel CPU bus access.
The order in which the bus blocks are specified defines which part of the address space a Bus Block occupies. The lowest addressed Bus Block is defined first, and the highest addressed Bus Block is defined last. The top-to-bottom order in which Bus Blocks are defined also controls the order in which UpdateMEM fills those Bus Blocks with data.