MC68HC705KJ1 Datasheet, PDF (33/108 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Chapter 4
Central Processor Unit (CPU)
4.1 Introduction
The central processor unit (CPU) consists of a CPU control unit, an arithmetic/logic unit (ALU), and five
CPU registers. The CPU control unit fetches and decodes instructions. The ALU executes the
instructions. The CPU registers contain data, addresses, and status bits that reflect the results of CPU
operations.
4.2 Features
Features of the CPU include:
• 4.0-MHz bus frequency on standard part
• 8-bit accumulator
• 8-bit index register
• 11-bit program counter
• 6-bit stack pointer
• Condition code register with five status flags
• 62 instructions
• 8 addressing modes
• Power-saving stop, wait, halt, and data-retention modes
The programming model is shown in Figure 4-1.
4.3 CPU Control Unit
The CPU control unit fetches and decodes instructions during program operation. The control unit selects
the memory locations to read and write and coordinates the timing of all CPU operations.
4.4 Arithmetic/Logic Unit
The arithmetic/logic unit (ALU) performs the arithmetic, logic, and manipulation operations decoded from
the instruction set by the CPU control unit. The ALU produces the results called for by the program and
sets or clears status and control bits in the condition code register (CCR).
MC68HC705KJ1 • MC68HRC705KJ1 • MC68HLC705KJ1 Data Sheet, Rev. 4.1
Freescale Semiconductor
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