Making Connections

orangesvetElectronics - Devices

Nov 8, 2013 (3 years and 9 months ago)

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Chapter Four

Making Connections

Objective


สามารถระบ

องค์ประกอบทั้ง
4

ของมาตรฐานการเชื่อมต่อ


สามารถอธิบายโอเปอร์เรชั่นพื้นฐานของ
EIA
-
232
F
และมาตรฐานการเชื่อมต่อ
แบบ
USB


สามารถวิเคราะห์ความแตกต่างระหว่างการเชื่อมแต่แบบฮาร์พด

เพล็ก และฟ

ลด

เพล็ก


สามารถบอกข้อดีของมาตรฐานการเชื่อมต่อของ
FireWire, SCSI, InfiniBand
และ
Fibre Channel


สามารถอธิบายค

ณลักษณะร

ปแบบการเชื่อมต่อข้อม

ลของอะซิงโครนัส
,
ซิงโครนัส
และ โอโซโครนัส


สามารถระบ

ลักษณะการท างานของการเชื่อมต่อเทอร์มินัลกับเมนเฟรม และ
สามารถวิเคราะห์ได้ว่าเหต

ใดจึงมีความแตกต่าง กับการเชื่อมต่อคอมพิวเตอร์
ประเภทอื่นๆ

Chapter Four

Making
Connections

Introduction


Connecting peripheral devices to a computer has, in
the past, been a fairly challenging task


Newer interfaces have made this task much easier


Let’s examine the interface between a computer and a
device. This interface occurs primarily at the
physical layer

Chapter Four
-

Making Connections


Interface Standards


There are essentially two types of standards


Official standards, created by standards making
organizations such as ITU (International
Telecommunications Union), IEEE (Institute for Electrical
and Electronics Engineers), EIA (Electronics Industries
Association), ISO (International Organization for
Standards), and ANSI (American National Standards
Institute)


De
-
facto standards


protocols created by other groups that
are not official standards but because of their widespread
use, become “almost” standards

Chapter Four
-

Making Connections


Interface Standards


There are four possible components to an interface
standard:


Electrical component


Mechanical component


Functional component


Procedural component

Chapter Four
-

Making Connections


The Four Components


The
electrical component

deals with voltages, line
capacitance, and other electrical characteristics


The
mechanical component

deals with items such as
the connector or plug description.

Chapter Four
-

Making Connections


The Four Components


The
functional component

describes the function of
each pin or circuit that is used in a particular interface


The
procedural component

describes how the
particular circuits are used to perform an operation

Chapter Four
-

Making Connections


Two Example Interfaces


In order to better understand the four components of
an interface, let’s examine two popular interface
standards


EIA
-
232F


an older standard originally designed to
connect a modem to a computer


USB (Universal Serial Bus)


a newer standard that is
much more powerful than EIA
-
232F

Chapter Four
-

Making Connections


RS
-
232 and EIA
-
232F


Originally named RS
-
232 but has gone through many
revisions


The electrical component is defined by another
standard: V.28


The mechanical component is often defined by ISO
2110, the DB
-
25 connector. The DB
-
9 connector is
now more common than the DB
-
25.

Chapter Four
-

Making Connections


Chapter Four
-

Making Connections


RS
-
232 and EIA
-
232F


The functional and procedural components are
defined by the V.24 standard


For example, V.24 defines the function of each of the
pins on the DB
-
9 connector, as shown on the next
slide

Chapter Four
-

Making Connections


RS
-
232 and EIA
-
232F

Chapter Four
-

Making Connections


RS
-
232 and EIA
-
232F


The next slide shows an example of the procedural
dialog that can be used to create a connection
between two endpoints


Note the level of complexity needed to establish a
full
-
duplex connection

Chapter Four
-

Making Connections


Chapter Four
-

Making Connections


Universal Serial Bus (USB)


The USB interface is a modern standard for
interconnecting a wide range of peripheral devices to
computers


Supports plug and play


Can daisychain multiple devices


USB 2.0 can support 480 Mbps (USB 1.0 is only 12
Mbps)

Chapter Four
-

Making Connections


Universal Serial Bus (USB)


The USB interface defines all four components


The electrical component defines two wires VBUS
and Ground to carry a 5 volt signal, while the D+ and
D
-

wires carry the data and signaling information


The mechanical component precisely defines the size
of four different connectors and uses only four wires
(the metal shell counts as one more connector)

Chapter Four
-

Making Connections


Universal Serial Bus (USB)

Chapter Four
-

Making Connections


Universal Serial Bus (USB)


The functional and procedural components are fairly
complex but are based on the polled bus


The computer takes turns asking each peripheral if it
has anything to send


More on polling near the end of this chapter

Chapter Four
-

Making Connections


Asynchronous Connections


A type of connection defined at the data link layer


To transmit data from sender to receiver, an
asynchronous connection creates a one
-
character
package called a frame


Added to the front of the frame is a Start bit, while a
Stop bit is added to the end of the frame


An optional parity bit can be added which can be
used to detect errors

Chapter Four
-

Making Connections


Asynchronous Connections

Chapter Four
-

Making Connections


Asynchronous Connections

Chapter Four
-

Making Connections


Asynchronous Connections


The term asynchronous is misleading here because
you must always maintain synchronization between
the incoming data stream and the receiver


Asynchronous connections maintain synchronization
by using small frames with a leading start bit

Chapter Four
-

Making Connections


Asynchronous Transmission

Synchronous Connections


A second type of connection defined at the data link
layer


A synchronous connection creates a large frame that
consists of header and trailer flags, control
information, optional address information, error
detection code, and data


A synchronous connection is more elaborate but
transfers data in a more efficient manner

Chapter Four
-

Making Connections


Synchronous Connections

Chapter Four
-

Making Connections


Synchronous Transmission

Isochronous Connections


A third type of connection defined at the data link
layer used to support real
-
time applications


The data must be delivered at just the right speed
(real
-
time)


not too fast and not too slow


Typically an isochronous connection must allocate
resources on both ends to maintain real
-
time


USB (and Firewire) can both support isochronous


Chapter Four
-

Making Connections


Half Duplex, Full Duplex, and Simplex
Connections


A half duplex connection transmits data in both
directions but in only one direction at a time


A full duplex connection transmits data in both
directions and at the same time


A simplex connection can transmit data in only one
direction


Chapter Four
-

Making Connections



Simplex

Half Duplex, Full Duplex, and Simplex
Connections


Half
-
Duplex

Half Duplex, Full Duplex, and Simplex
Connections


Full
-
Duplex

Half Duplex, Full Duplex, and Simplex
Connections

Terminal
-
to
-
Mainframe Connections


A
point
-
to
-
point connection

is a direct, unshared
connection between a terminal and a mainframe
computer


A
multipoint connection

is a shared connection
between multiple terminals and a mainframe
computer


The mainframe is the
primary

and the terminals are
the
secondaries


Chapter Four
-

Making Connections


Terminal
-
to
-
Mainframe Connections

Chapter Four
-

Making Connections


Terminal
-
to
-
Mainframe Connections


To allow a terminal to transmit data to a mainframe,
the mainframe must poll the terminal


Two basic forms of polling: roll
-
call polling and hub
polling


In roll
-
call polling, the mainframe polls each terminal
in a round
-
robin fashion


In hub polling, the mainframe polls the first terminal,
and this terminal passes the poll onto the next
terminal

Chapter Four
-

Making Connections


Terminal
-
to
-
Mainframe Connections

Chapter Four
-

Making Connections



Roll call polling

Making Computer Connections In Action


The back panel of a personal computer has many
different types of connectors, or connections:


RS
-
232 connectors


USB connectors


Parallel printer connectors


Serial port connectors

Chapter Four
-

Making Connections


Making Computer Connections In Action

Chapter Four
-

Making Connections


Making Computer Connections In Action


1 and 2


DIN connectors for keyboard and mouse


3


USB connectors


4 and 6


DB
-
9 connectors


5


Parallel port connector (Centronics)


7, 8, and 9


audio connectors


Will Bluetooth or ??? replace these someday?

Chapter Four
-

Making Connections


Making Computer Connections In Action


A company wants to transfer files that are typically
700K chars in size


If an asynchronous connection is used, each character
will have a start bit, a stop bit, and maybe a parity bit


700,000 chars * 11 bits/char (8 bits data + start + stop
+ parity) = 7,700,000 bits

Chapter Four
-

Making Connections


Making Computer Connections In Action


If a synchronous connection is used, assume
maximum payload size


1500 bytes


To transfer a 700K char file requires 467 1500
-
character (byte) frames


Each frame will also contain 1
-
byte header, 1
-
byte
address, 1
-
byte control, and 2
-
byte checksum, thus 5
bytes overhead

Chapter Four
-

Making Connections


Making Computer Connections In Action


1500 bytes payload + 5 byte overhead = 1505 byte
frames


467 frames * 1505 bytes/frame = 716,380 bytes, or
5,731,040 bits


Significantly less data using synchronous connection

Chapter Four
-

Making Connections


Workshop


จงอธิบายความแตกต

างในการเชื่อมต

อแบบ
Asynchronous, Synchronous
และ
Isochronous


การเชื่อมต

อแบบ
Asynchronous

มีบิตใดที่เพิ

มเติมขึ


นอกเหนือจากตัวอักษรปกติที่ใช้ในการส

งข้อมูล


จงบอกความแตกต

างระหว

างการสื่อสารแบบ
half
-
duplex
และ
full
-
duplex


จงบอกความแตกต

างระหว

างการเชื่อมต

อแบบ
point
-
to
-
point
และ
multipoint

Workshop


วิธีที่เมนเฟรมคอมพิวเตอร์ ติดต

อสอบถามเครื่องเทอร์มินัล
เพื่อส

งข้อมูล เรียกว

าอะไร


DTE
และ
DCE
คืออะไร


หากต้องการส

งข้อความตัวอักษร
1000
ตัวอักษร แบบ
7
บิต ต้อง
ใช้บิตในการส

งแบบ

Asynchronous
ทั

งหมดจ านวนก
ี่
บิต และ
สมมติว

า การส

งทั


1000
ตัวอักษรนั

น ใช้เฟรมในการส

งแบบ
Synchronous

เพียง
1
เฟรมเท

านั

น จะต้องใช้บิตในการส

งแบบ

Synchronous
ทั

งหมดจ านวนก
ี่
บิต

แสดงวิธีการค านวณโดย
ละเอียด