Having an address bus of 16-bits wide, the typical HCS08 Core architecture limits the available CPU addressable space to 64K bytes. However, some special HCS08 MCUs, like the MC9S08QE128 which contains a MMU (Memory Management Unit), extends the processor's ability of addressing up to 4M memory space.
On these derivatives, memory can be accesses using the paging mechanism, using the linear memory access mechanism or directly, if the address is below 64K.
To avoid common pitfalls and to detect where there may be room for code optimizations, you need to have a complete understanding of your application. Thus, it is essential to know how to correctly access a given memory location and how CodeWarrior distributes your code between these three memory categories.
The following sections in this chapter introduce the notions of these three kinds of memory and highlight their differences.