Page 61 - DCAP210_INTRODUCTION__TO_MICROPROCESSORS

Unit 4: Microprocessor Architecture

The 8085 uses three separate buses to perform its operations: Notes
• The address bus
• The data bus
• The control bus

4.1.1 The Address Bus

16 bits wide (A0 A1…A15): Therefore, the 8085 can access locations with numbers from 0 to
65,536. Or, the 8085 can access a total of 64K addresses.
“Unidirectional”: Information flows out of the microprocessor and into the memory or peripherals.
When the 8085 wants to access a peripheral or a memory location, it places the 16-bit address on
the address bus and then sends the appropriate control signals.

4.1.2 The Data Bus
8 bits wide (D0 D1…D7) & “Bi-directional”, Information flows both ways between the
microprocessor and memory or I/O. The 8085 uses the data bus to transfer the binary information.

Since the data bus has 8-bits only, the 8085 can manipulate data 8 bits at a time only.
4.1.3 The Control Bus

There is no real control bus. Instead, the control bus is made up of a number of single bit control
signals.

There are eight datelines’, D0 through D7, in the 8085 microprocessor. They
are shared, or multiplexed with the eight low order address lines, A0 through
A7, and are called AD0 through AD7 on the...
Accessing Information in Memory:
For the microprocessor to access (Read or Write) information in memory (RAM or ROM), it needs
to do the following:
• Select the right memory chip (using part of the address bus).
• Identify the memory location (using the rest of the address bus).
• Access the data (using the data bus).
Microprocessors function as the “brain” of a computer system. As technology has progressed,
microprocessors have become faster, smaller and capable of doing more work per clock cycle.
However, when trying to choose a microprocessor, it is difficult to understand what the
designations mean. Should you choose an x64 processor or an x86 processor? Is a dual-core fast
enough, or do you need a quad-core processor? Understanding the differences in microprocessor
architecture will aid in the decision-making process.

The latest technological changes in 32-and 64-bit microprocessors.

4.1.4 X64 vs X86

A microprocessor may be listed for sale as an “x86 processor” or an “x64 processor.” What is the
difference, though?

An “x86” processor is a microprocessor that is capable of processing information in 32-bit pieces
(called “instructions”). Each “bit” is a piece of information that the computer uses to transmit
information, run computations and perform other such processes. A processor using x86
architecture is considered to be a successor technology to the original microprocessors used in

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