COP8SE datasheet(35/47 Pages) NSC

35 / 47 page

12.0 Instruction Set

12.1 INTRODUCTION

This section defines the instruction set of the COPSAx7

Family members. It contains information about the instruc-

tion set features, addressing modes and types.

12.2 INSTRUCTION FEATURES

The strength of the instruction set is based on the following

features:

•

Mostly single-byte opcode instructions minimize program

size.

•

One instruction cycle for the majority of single-byte in-

structions to minimize program execution time.

•

Many single-byte, multiple function instructions such as

DRSZ.

•

Three memory mapped pointers: two for register indirect

addressing, and one for the software stack.

•

Sixteen memory mapped registers that allow an opti-

mized implementation of certain instructions.

•

Ability to set, reset, and test any individual bit in data

memory address space, including the memory-mapped

I/O ports and registers.

•

with optional automatic post-incrementing or decrement-

ing of the register pointer. This allows for greater effi-

ciency (both in cycle time and program code) in loading,

walking across and processing fields in data memory.

•

Unique instructions to optimize program size and

throughput efficiency. Some of these instructions are

DRSZ, IFBNE, DCOR, RETSK, VIS and RRC.

12.3 ADDRESSING MODES

The instruction set offers a variety of methods for specifying

memory addresses. Each method is called an addressing

mode. These modes are classified into two categories: oper-

and addressing modes and transfer-of-control addressing

modes. Operand addressing modes are the various meth-

ods of specifying an address for accessing (reading or writ-

ing) data. Transfer-of-control addressing modes are used in

conjunction with jump instructions to control the execution

sequence of the software program.

12.3.1 Operand Addressing Modes

The operand of an instruction specifies what memory loca-

tion is to be affected by that instruction. Several different op-

erand addressing modes are available, allowing memory lo-

cations to be specified in a variety of ways. An instruction

can specify an address directly by supplying the specific ad-

dress, or indirectly by specifying a register pointer. The con-

tents of the register (or in some cases, two registers) point to

the desired memory location. In the immediate mode, the

data byte to be used is contained in the instruction itself.

Each addressing mode has its own advantages and disad-

vantages with respect to flexibility, execution speed, and pro-

gram compactness. Not all modes are available with all in-

structions. The Load (LD) instruction offers the largest

number of addressing modes.

The available addressing modes are:

•

Direct

•

Indirect

with

Post-Incrementing/

Decrementing

•

Immediate

•

Immediate Short

•

Indirect from Program Memory

The addressing modes are described below. Each descrip-

tion includes an example of an assembly language instruc-

tion using the described addressing mode.

Direct. The memory address is specified directly as a byte in

the instruction. In assembly language, the direct address is

written as a numerical value (or a label that has been defined

elsewhere in the program as a numerical value).

Example: Load Accumulator Memory Direct

LD A,05

Reg/Data

Contents

Memory

Before

After

Accumulator

XX Hex

A6 Hex

Memory Location

A6 Hex

0005 Hex

by the contents of the B Register or X register (pointer regis-

ter). In assembly language, the notation [B] or [X] specifies

which register serves as the pointer.

Example: Exchange Memory with Accumulator, B Indirect

X A,[B]

Reg/Data

Contents

Memory

Before

After

Accumulator

01 Hex

87 Hex

Memory Location

87 Hex

01 Hex

0005 Hex

B Pointer

05 Hex

Decrementing. The relevant memory address is specified

by the contents of the B Register or X register (pointer regis-

ter). The pointer register is automatically incremented or

decremented after execution, allowing easy manipulation of

memory blocks with software loops. In assembly language,

the notation [B+], [B−], [X+], or [X−] specifies which register

serves as the pointer, and whether the pointer is to be incre-

mented or decremented.

Example: Exchange Memory with Accumulator, B Indirect

with Post-Increment

X A,[B+]

Reg/Data

Contents

Memory

Before

After

Accumulator

03 Hex

62 Hex

Memory Location

62 Hex

03 Hex

0005 Hex

B Pointer

05 Hex

06 Hex

Intermediate. The data for the operation follows the instruc-

tion opcode in program memory. In assembly language, the

number sign character (#) indicates an immediate operand.

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