Page 136 - DCAP210_INTRODUCTION__TO_MICROPROCESSORS

Introduction to Microprocessors

Notes 4. A program sequence can be changed either conditionally or by testing for a given data
condition.
The Machine Control instructions are as follows:

EI: Enable Interrupt System
DI: Disable Interrupt System
HLT: Halt

NOP: No Operation
Intel was the first company to produce a microprocessor for commercial use.
Called the 4004, it was released in the early 1970s and contained slightly more
than 2,000 transistors.

9.6 Stack I/O Operations

The following instructions affect the Stack and/or Stack Pointer:

PUSH: Push Two bytes of Data onto the Stack
POP: Pop Two Bytes of Data off the Stack
XTHL: Exchange Top of Stack with H & L

SPHL: Move content of H & L to Stack Pointer
The I/O instructions are as follows:
IN: Initiate Input Operation

OUT: Initiate Output Operation
9.7 Instruction Format

An instruction is a command to the microprocessor to perform a given task on a specified data.
Each instruction has two parts: one is task to be performed, called the operation code (opcode),
and the second is the data to be operated on, called the operand. The operand (or data) can be
specified in various ways. It may include 8-bit (or 16-bit) data, an internal register, a memory
location, or 8-bit (or 16-bit) address.
In some instructions, the operand is implicit.

9.7.1 Instruction Word Size
The 8085 instruction set is classified into the following three groups according to word size:

1. One-word or 1-byte instructions
2. Two-word or 2-byte instructions
3. Three-word or 3-byte instructions
In the 8085, “byte” and “word” are synonymous because it is an 8-bit microprocessor.

However, instructions are commonly referred to in terms of bytes rather than words.
One-Byte Instructions
A 1-byte instruction includes the opcode and operand in the same byte. Operand(s) are internal
register and are coded into the instruction.

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