Interconnecting
System Components
Buses-
The
address bus is the set of wires that carries the addressing information used to
describe the memory location to which the data is being sent or from which the
data is being retrieved. As with the data bus, each wire in an address bus
carries a single bit of information. This single bit is a single digit in the
address. The more wires (digits) used in calculating these addresses, the greater
the total number of address locations. The size (or width) of the address bus
indicates the maximum amount of RAM that a chip can address.
The highway analogy can be used to show how the
address bus fits in. If the data bus is the highway
and the size of the data bus is equivalent to the
number of lanes, the address bus relates to the house
number or street address. The size of the address
bus is equivalent to the number of digits in the
house address number. For example, if you live on a
street in which the address is limited to a two digit (base 10) number, no more
than 100 distinct addresses (00–99) can exist for that street (102).
Add another digit, and the number of available
addresses increases to 1,000 (000–999), or 103.
Computers use the binary (base 2) numbering system,
so a two-digit number provides only four
unique addresses (00, 01, 10, and 11) calculated as
22. A three-digit number provides only eight
addresses (000–111), which is 23. For example, the
8086 and 8088 processors use a 20-bit address
bus that calculates as a maximum of 220 or
1,048,576 bytes (1MB) of address locations. Table 3.10
describes
the memory-addressing capabilities of processors.
Interfacing
buses- On
a system that has multiple buses, circuitry must be provided by the chipset to
connect the buses and allow devices on one to talk to devices on the other.
This device is called a "bridge", the same name used to refer to a
piece of networking hardware that connects two dissimilar networks. By far the
most commonly found bridge is the PCI-ISA bridge, which is part of the system chipset on a
Pentium or Pentium Pro PC. The PCI bus also has a bridge to the processor bus;
you can see these devices under "System devices" in the Device
Manager in Windows 95.
The system bus is a cable which carries data
communication between the major components of the computer, including the
microprocessor. Not all of the communication that uses the bus involves the
CPU, although naturally the examples used in this tutorial will centre on such
instances.
The system bus consists of three different groups
of wiring, called the data bus, control bus and address bus. These all have
seperate responsibilities and characteristics, which can be outlined as
follows:
Bus
Formats –
Address Bus
The address bus contains the connections between the microprocessor and memory that carry the signals relating to the addresses which the CPU is processing at that time, such as the locations that the CPU is reading from or writing to. The width of the address bus corresponds to the maximum addressing capacity of the bus, or the largest address within memory that the bus can work with. The addresses are transferred in binary format, with each line of the address bus carrying a single binary digit. Therefore the maximum address capacity is equal to two to the power of the number of lines present (2^lines).
The address bus contains the connections between the microprocessor and memory that carry the signals relating to the addresses which the CPU is processing at that time, such as the locations that the CPU is reading from or writing to. The width of the address bus corresponds to the maximum addressing capacity of the bus, or the largest address within memory that the bus can work with. The addresses are transferred in binary format, with each line of the address bus carrying a single binary digit. Therefore the maximum address capacity is equal to two to the power of the number of lines present (2^lines).
This concludes the look at the simplified model
processor that will be used for the remainder of this tutorial. The next
section will look at the instruction
execution process, and how these different parts work together to
execute programs. However, before that, there's a chance to test what you've
learnt in this section regarding processor architecture. Click the next arrow
below to take a short quiz relatin.
Data Bus
This is used for the exchange of data between the processor, memory and peripherals, and is bi-directional so that it allows data flow in both directions along the wires. Again, the number of wires used in the data bus (sometimes known as the 'width') can differ. Each wire is used for the transfer of signals corresponding to a single bit of binary data. As such, a greater width allows greater amounts of data to be transferred at the same time.
This is used for the exchange of data between the processor, memory and peripherals, and is bi-directional so that it allows data flow in both directions along the wires. Again, the number of wires used in the data bus (sometimes known as the 'width') can differ. Each wire is used for the transfer of signals corresponding to a single bit of binary data. As such, a greater width allows greater amounts of data to be transferred at the same time.
Control Bus
The control bus carries the signals relating to the control and co-ordination of the various activities across the computer, which can be sent from the control unit within the CPU. Different architectures result in differing number of lines of wire within the control bus, as each line is used to perform a specific task. For instance, different, specific lines are used for each of read, write and reset requests.
The control bus carries the signals relating to the control and co-ordination of the various activities across the computer, which can be sent from the control unit within the CPU. Different architectures result in differing number of lines of wire within the control bus, as each line is used to perform a specific task. For instance, different, specific lines are used for each of read, write and reset requests.
Interfacing
keyboard- The
keyboard uses a special, dedicated interface to talk to the PC. The basic
design and operation of this interface is largely unchanged since the days of
the old IBM PC/AT of the mid-1980s. Only in the last few years has the
availability of the universal serial bus (USB) on newer systems created an
alternative way of attaching a keyboard to the PC. The conventional keyboard
interface is still used in almost all PCs, however, despite USB's growing
popularity.
The traditional keyboard interface is in some ways
similar to a "stripped-down version" of a regular serial (COM) port.
Communication between the keyboard and the PC is accomplished over the lines in
the keyboard cable, which connect the internal controller in the keyboard with
a matching device on the motherboard, called the keyboard controller. This is
really a misnomer of sorts, since it's arguable that the chip within the system
doesn't control the keyboard; the chip within the keyboard does! It would
probably be better if it were called the keyboard interface controller,
actually.
Motherboards in older PCs, which were designed
before the invention of integrated chipsets, used an Intel 8042 chip for their
keyboard controller. This became the standard on virtually all PCs. Today,
motherboards don't necessarily include a physical 8042 chip, but they emulate
its functionality for the sake of compatibility. The keyboard controller is
also responsible for other tasks within the PC; read more about it here.
All keyboards that use standard keyboard
connectors to attach to the motherboard use the regular keyboard
interface. This is true whether they use the larger 5-pin DIN connector, or the
smaller, 6-pin mini-DIN. Communication over the interface is accomplished using
two signaling lines, and is governed by a number of special rules and protocols,
as described in the page on
interface signaling. On modern PCs the communication is
bi-directional, with the keyboard's internal controller and the motherboard's
keyboard controller each able to send and receive commands over the interface.
DISPLAY-
A display device is an output device for
presentation of information
in visualHYPERLINK
"http://en.wikipedia.org/wiki/Visual" HYPERLINK
"http://en.wikipedia.org/wiki/Visual"HYPERLINK
"http://en.wikipedia.org/wiki/Visual" HYPERLINK "http://en.wikipedia.org/wiki/Display_device"HYPERLINK
"http://en.wikipedia.org/wiki/Visual" HYPERLINK
"http://en.wikipedia.org/wiki/Visual"HYPERLINK
"http://en.wikipedia.org/wiki/Visual"[1] or tactile form (the latter
used for example in tactile electronic
displays for blind people).[2] When the input
information is supplied as an electrical signal, the display is called an electronic
display.
Common applications for electronic visual
displays are televisions
or computer monitors.
auxiliary storage devices and printers.- Auxiliary
storage units behave in a manner similar to other I/O devices, but users do not
interact directly with them. If you were to place yourself inside the computer,
in many ways you would not be able to distinguish among the various kinds of
I/O equipment. Auxiliary storage equipment has data transmission rates that may
be significantly higher than other I/O devices but are still much slower than
the internal speeds of the processor; hence, many of the techniques already
discussed, such as buffering, are used.
Auxiliary storage serves two main purposes: it
serves as an extension of the main memory or as a medium to permanently archive
information. The computer can use it as a memory extension for its own purposes
outside the control of the user. Called virtual memory, this concept will be
discussed later. On the other hand, the user can employ the extra storage to
maintain almost limitless information.
Printer- An external
hardware
device responsible for taking computer data and generating a hard copy
of that data. Printers are one of the most used peripherals on computers and
are commonly used to print text, images, and photos. In the picture to the
right, is a visual example of the Lexmark Z605 Inkjet printer
and is an example of what a printer may look like.
I/O
cards in personal computers- Circuit Specialists has an extensive
catalog of affordable, high-quality PC-based I/O cards for expanding existing
features or for adding new features not offered on the motherboard. Common I/O
expansion cards include network, modem, and storage area network (SAN) cards.
Take a look at our compact and low-profile expansion cards if you have a
smaller chassis. If you're looking for more slots, browse our PCI-to-PCI
expansion systems, which allow you to add four or thirteen PCI slots to your computer.
Introduction
to Microprocessors and Microcontrollers-
Microprocessors -A silicon chip that contains a CPU. In the world of personal computers,
the terms microprocessor and CPU are used interchangeably. At the heart of all
personal computers and most workstations sits a
microprocessor. Microprocessors also control the logic of almost all digital devices, from clock radios
to fuel-injection systems
for automobiles.
Three basic characteristics differentiate
microprocessors:
· Instruction set:
The set of instructions that the microprocessor can execute.
· clock speed
: Given in megahertz (MHz),
the clock speed determines how many instructions per second the processor can execute.
In both cases, the higher the value, the more
powerful the CPU. For example, a 32-bit microprocessor that
runs at 50MHz is more
powerful than a 16-bit microprocessor that runs at 25MHz.
In addition to bandwidth and clock speed,
microprocessors are classified as being either RISC (reduced instruction
set computer)
or CISC (complex instruction
set computer).
Microcontroller-
A microcontroller (sometimes abbreviated µC, uC or MCU)
is a small computer on a single integrated circuit containing
a processor core, memory, and programmable input/output peripherals.
Program memory in the form of NOR flash
or OTP ROM
is also often included on chip, as well as a typically small amount of RAM.
Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or
other general purpose applications.
Microcontrollers are used in automatically
controlled products and devices, such as automobile engine control systems,
implantable medical devices, remote controls, office machines, appliances,
power tools, toys and other embedded systems. By
reducing the size and cost compared to a design that uses a separate
microprocessor, memory, and input/output devices, microcontrollers make it
economical to digitally control even more devices and processes. Mixed signal
microcontrollers are common, integrating analog components needed to control
non-digital electronic systems.
Some microcontrollers may use four-bit words
and operate at clock rate
frequencies as low as 4 kHz, for low power consumption (single-digit
milliwatts or microwatts). They will generally have the ability to retain
functionality while waiting for an event such as a button press or other
interrupt; power consumption while sleeping (CPU clock and most peripherals
off) may be just nanowatts, making many of them well suited for long lasting
battery applications. Other microcontrollers may serve performance-critical
roles, where they may need to act more like a digital signal
processor (DSP), with higher clock speeds and power consumption.
introduction to 8085 micropocesor- Today
the microprocessor based products have revolutionized every area of human
activity and have made a deep impact on quality of life. Right from small chip
to supercomputer Microprocessor have become an integral part of the system.
Microprocessor evolved from the developments in computer. One such
microprocessor is Intel’s 8085, which is most popularly used and regarded as a
basic microprocessor. The microprocessors operation can be described through
the organization of computer model.
Generally a computer organization is as follows
INPUT>
ALU+CONTROL UNIT+MEMORY> OUTPUT
(1) (2) (3)
(1) (2) (3)
Unit 2 is generally replaced with microprocessor. So
a microprocessor can be represented as :
Microprocessor=ALU+Registers+Program
Counter+Control and Timing circuit+Stack Pointer +Interrupt Circuit.
The hardware of the 8085 microprocessor can be
easily understood from the description of the programming model.
examples of few instructions to understand addressing
techniques- Addressing
modes are the method used to determine which part of memory is being referred
to by a machine instruction. There are various types of addressing modes. Which
addressing mode is used is dependent on what type of computer
architecture is being used.
Random access memory (RAM) is the primary area of
memory for a computer. This is where any application must be loaded to if it is
to be run. The central processing
unit (CPU)
reads machine instructions from the RAM and acts on those instructions. This is
what happens whenever any application is run on a computer.
The machine instructions given to the CPU often
must refer to specific portions of the RAM. In order to do this, the CPU must
have a way of knowing which portion of RAM the machine instruction is referring
to. This is where addressing modes come into play.
Difference between microprocessor and
microcontrollers- Microprocessor is an
IC which has only the CPU inside them i.e. only the processing powers such as
Intel’s Pentium 1,2,3,4, core 2 duo, i3, i5 etc. These microprocessors don’t
have RAM, ROM, and other peripheral on the chip. A system designer has to add
them externally to make them functional. Application of microprocessor includes
Desktop PC’s, Laptops, notepads etc.
But this is not the case with Microcontrollers.
Microcontroller has a CPU, in addition with a fixed amount of RAM, ROM and
other peripherals all embedded on a single chip. At times it is also termed as
a mini computer or a computer on a single chip. Today different manufacturers
produce microcontrollers with a wide range of features available in different
versions. Some manufacturers are ATMEL, Microchip, TI, Freescale, Philips,
Motorola etc.
Microcontrollers are designed to perform specific
tasks. Specific means applications where the relationship of input and output
is defined. Depending on the input, some processing needs to be done and output
is delivered. For example, keyboards, mouse, washing machine, digicam,
pendrive, remote, microwave, cars, bikes, telephone, mobiles, watches, etc.
Since the applications are very specific, they need small resources like RAM,
ROM, I/O ports etc and hence can be embedded on a single chip. This in turn
reduces the size and the cost.
Microprocessor find applications where tasks are
unspecific like developing software, games, websites, photo editing, creating
documents etc. In such cases the relationship between input and output is not
defined. They need high amount of resources like RAM, ROM, I/O ports etc.
The clock speed of the Microprocessor is quite high
as compared to the microcontroller. Whereas the microcontrollers operate from a
few MHz to 30 to 50 MHz, today’s microprocessor operate above 1GHz as they
perform complex tasks.
