SC9RS08KA2 datasheet(58/134 Pages) FREESCALE

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Chapter 8 Central Processor Unit (RS08CPUV1)

SC9RS08KA2 Series Data Sheet, Rev. 1

Freescale Semiconductor

Figure 8-1. CPU Registers

In addition to the CPU registers, there are three memory mapped registers that are tightly coupled with the

core address generation during data read and write operations. They are the indexed data register (D[X]),

the index register (X), and the page select register (PAGESEL). These registers are located at $000E,

$000F, and $001F, respectively.

Figure 8-2. Memory Mapped Registers

8.2.1

Accumulator (A)

This general-purpose 8-bit register is the primary data register for RS08 MCUs. Data can be read from

memory into A with a load accumulator (LDA) instruction. The data in A can be written into memory with

a store accumulator (STA) instruction. Various addressing mode variations allow a great deal of flexibility

in specifying the memory location involved in a load or store instruction. Exchange instructions allow

values to be exchanged between A and SPC high (SHA) and also between A and SPC low (SLA).

Arithmetic, shift, and logical operations can be performed on the value in A as in ADD, SUB, RORA,

INCA, DECA, AND, ORA, EOR, etc. In some of these instructions, such as INCA and LSLA, the value

in A is the only input operand and the result replaces the value in A. In other cases, such as ADD and AND,

there are two operands: the value in A and a second value from memory. The result of the arithmetic or

logical operation replaces the value in A.

Some instructions, such as memory-to-memory move instructions (MOV), do not use the accumulator.

DBNZ also relieves A because it allows a loop counter to be implemented in a memory variable rather than

the accumulator.

During reset, the accumulator is loaded with $00.

SPC

CARRY

ZERO

ACCUMULATOR

SHADOW PROGRAM COUNTER

PROGRAM COUNTER

CCR

CONDITION CODE REGISTER

INDEXED DATA REGISTER D[X] (location $000E)

INDEX REGISTER

X (location $000F)

PAGE SELECT REG

PAGESEL (location $001F)

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