MC705P6ACPE Datasheet, PDF (71/98 Pages) Freescale Semiconductor, Inc – M68HC05 Microcontrollers

Chapter 13
Instruction Set
13.1 Introduction
The MCU instruction set has 62 instructions and uses eight addressing modes. The instructions include
all those of the M146805 CMOS Family plus one more: the unsigned multiply (MUL) instruction. The MUL
instruction allows unsigned multiplication of the contents of the accumulator (A) and the index register (X).
The high-order product is stored in the index register, and the low-order product is stored in the
accumulator.
13.2 Addressing Modes
The CPU uses eight addressing modes for flexibility in accessing data. The addressing modes provide
eight different ways for the CPU to find the data required to execute an instruction. The eight addressing
modes are:
• Inherent
• Immediate
• Direct
• Extended
• Indexed, no offset
• Indexed, 8-bit offset
• Indexed, 16-bit offset
• Relative
13.2.1 Inherent
Inherent instructions are those that have no operand, such as return from interrupt (RTI) and stop (STOP).
Some of the inherent instructions act on data in the CPU registers, such as set carry flag (SEC) and
increment accumulator (INCA). Inherent instructions require no operand address and are one byte long.
13.2.2 Immediate
Immediate instructions are those that contain a value to be used in an operation with the value in the
accumulator or index register. Immediate instructions require no operand address and are two bytes long.
The opcode is the first byte, and the immediate data value is the second byte.
13.2.3 Direct
Direct instructions can access any of the first 256 memory locations with two bytes. The first byte is the
opcode, and the second is the low byte of the operand address. In direct addressing, the CPU
automatically uses $00 as the high byte of the operand address.
MC68HC705P6A Advance Information Data Sheet, Rev. 2.1
Freescale Semiconductor
71