MC9RS08KA2 Datasheet, PDF (27/132 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 4 Memory
4.2 Unimplemented Memory
Attempting to access either data or an instruction at an unimplemented memory address will cause reset.
4.3 Indexed/Indirect Addressing
Register D[X] and register X together perform the indirect data access. Register D[X] is mapped to address
$000E. Register X is located in address $000F. The 8-bit register X contains the address that is used when
register D[X] is accessed. Register X is cleared to zero upon reset. By programming register X, any
location on the first page ($0000–$00FF) can be read/written via register D[X]. Figure 4-2 shows the
relationship between D[X] and register X. For example, in HC08/S08 syntax lda ,x is comparable to lda
D[X] in RS08 coding when register X has been programmed with the index value.
The physical location of $000E is in RAM. Accessing the location through D[X] returns $000E RAM
content when register X contains $0E. The physical location of $000F is register X, itself. Reading the
location through D[X] returns register X content; writing to the location modifies register X.
$0000
$000E
$000F
D[X]
Register X
Address indicated in
Register X
$00FF
$0100
Content of this location can be accessed via D[X]
Register X can specify
any location between
$0000–$00FF
Figure 4-2. Indirect Addressing Registers
4.4 RAM and Register Addresses and Bit Assignments
The fast access RAM area can be accessed by instructions using tiny, short, and direct addressing mode
instructions. For tiny addressing mode instructions, the operand is encoded along with the opcode to a
single byte.
MC9RS08KA2 Series Data Sheet, Rev. 2
Freescale Semiconductor
27