COP8SG National Semiconductor, COP8SG Datasheet - Page 46

• Manufacturer Part Number: COP8SG
• Description: 8-Bit CMOS ROM Based and OTP Microcontrollers with 8k to 32k Memory/ Two Comparators and USART
• Manufacturer: National Semiconductor

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14.0 Instruction Set
14.1 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.
14.2 INSTRUCTION FEATURES
The strength of the instruction set is based on the following
features:
14.3 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.
14.3.1 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.
• Mostly single-byte opcode instructions minimize program
• One instruction cycle for the majority of single-byte in-
• Many single-byte, multiple function instructions such as
• Three memory mapped pointers: two for register indirect
• Sixteen memory mapped registers that allow an opti-
• Ability to set, reset, and test any individual bit in data
• Register-Indirect LOAD and EXCHANGE instructions
• Unique instructions to optimize program size and
size.
structions to minimize program execution time.
DRSZ.
addressing, and one for the software stack.
mized implementation of certain instructions.
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.
throughput efficiency. Some of these instructions are
DRSZ, IFBNE, DCOR, RETSK, VIS and RRC.
46
The available addressing modes are:
• Direct
• Register B or X Indirect
• Register B or X Indirect with Post-Incrementing/
• 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
Register B or X Indirect. The memory address is specified
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
Register B or X Indirect with Post-Incrementing/
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
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.
Decrementing
LD A,05
X A,[B]
with Post-Increment
X A,[B+]
Memory Location
Memory Location
Memory Location
Accumulator
Accumulator
Accumulator
Reg/Data
0005 Hex
Reg/Data
0005 Hex
Reg/Data
0005 Hex
B Pointer
B Pointer
Memory
Memory
Memory
Contents
Contents
Contents
XX Hex
A6 Hex
01 Hex
87 Hex
05 Hex
03 Hex
62 Hex
05 Hex
Before
Before
Before
Contents
Contents
Contents
A6 Hex
A6 Hex
87 Hex
01 Hex
05 Hex
62 Hex
03 Hex
06 Hex
After
After
After