ANALOG AND DIGITAL PHYSICAL INTERFACES

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ANALOG AND DIGITAL PHYSICAL INTERFACES

• Habib Youssef, Ph.D
• youssef_at_ccse.kfupm.edu.sa
• Department of Computer Engineering
• King Fahd University of Petroleum and Minerals
• Dhahran, Saudi Arabia

COMPUTER NETWORK
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The RS-232/CCITT V.24 and V.28 Interface
RS-232/CCITT V.24
Computer
Computer
Data
Data
Modem
Modem
DTE
DTE
DCE
DCE
Out of Band Control
Out of Band Control
DTE Data Terminal Equipment DCE Data Circuit
Termination Equipment
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The RS-232/CCITT V.24 and V.28 Interface (Cont.)

• Data processing (DTE) to modem (DCE) interface
• The CCITT V.24 Recommendation defines the
  interchange circuits
• V.28 defines the electrical characteristics

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The RS-232/CCITT V.24 and V.28 Interface (Cont.)

• In EIA, known as RS-232-C (the third -C version
  of RS-232)
• More recent version of RS-232-D (now EIA-232-D)
• Sometimes TIA-232-D (Telecommunications Industry
  Association)

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The RS-232/CCITT V.24 and V.28 Interface (Cont.)

• A 25-pin connector/interface
• ISO 2110 is used
• Is not part of the RS-232-C standard
• Bit serial data (full duplex)
• Out of band control lines

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The RS-232/CCITT V.24 and V.28 With Null Modems
DCE
DTE
Null Modem
Data
Data
2
2
Data
Data
3
3
Req to Send
Req to Send
4
4
Clear to Send
Clear to Send
5
5
Data Set Ready
Data Set Ready
6
6
Signal Detect
Signal Detect
8
8
Data Terminal Ready
Data Terminal Ready
20
20
Signal Ground
7
7
Note There are many variations to Null Modem
Cross Connection
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Pin Assignments for V.24/EIA-232
Reserved for testing
Secn. CTS
Unassigned
Shield
Clear to Send
GND
Rx Data
Secn. Recv. Line Signal Detector
DCE Ready
Carrier Detect
Tx Data
Reg to Send
Reserved for testing
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
21
16
20
17
19
18
22
23
24
25
Transmitter signal element timing
Secondary RTS
Test Mode
Transmitter signal element timing
Remote Loopback
Data Signal Rate Select
Transmit signal element timing
Local Loopback
DTE Ready
Secondary received data
Ring Indicator
Secondary Tx Data
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RS-232/CCITT V.24 V.28 Related Products

• It is often convenient to switch RS-232/V.24
  signals from a computer to one of several devices
• For example, to different types of printers
• Simple multiple switches are available for this
  purpose

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RS-232/CCITT V.24 V.28 Related Products (Cont.)

• Specialized companies have been developed to
  handle the interface market with products such as
• Multiple switches
• RS-232/V.24 cables
• Null modems
• RS-232/V.24 gender changers
• Breakout boxes to monitor control signals

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Limitations of RS-232/V.28

• An upper data rate of about 20 kbit/s
• An upper cable length of about 50 to 100 feet
  (about 20 to 40 m)
• Some products are available to extend these, but
  a new approach is needed

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The Evolution of RS-232-C
RS-449 signals RS-422/423 electrical
(1977) RS-442 balanced circuits RS-443 unbalanced
circuits
RS-232-C

• RS-530 (1987)
• Balanced Circuits

• V.35
• Balanced Circuits

• EIA-232-D (1987)
• Unbalanced circuits

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Synchronous Transmission

• Has a known timing relationship between bits and
  characters
• Characters are sent one after the other
• The receiver recovers this timing from
  transitions in the arriving data

1
0
Start
End
Characters
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V.24/EIA-232 dial-up operation
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RS-423/CCITT V.10Single Ended Interchange
Circuit
Noise
Error
Recvr
Trans
Signal return
Note V.10 is the same as X.26 or RS-423-A
(unbalanced)
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RS-422/CCITT V.11 Differential Interchange
Circuit
Noise
Sensitive to differential signal
Recvr
Trans
Noise was rejected
Termination resistor
Note V.11 is the same as X.27 or RS-422-A
(balanced)
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CCITT X.21 Interface

• Physical-level interface between DTE and DCE
• For synchronous operations on public data
  networks
• X.21 uses control transitions and ASCII
  characters rather than using separate signal
  lines

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CCITT X.21 Interface (Cont.)

• The X.21 electrical characteristics are
• CCITT X.27 (balanced same as V.11 and RS-422)
• CCITT X.26 (unbalanced V.10 and RS-423)
• (Note For operation above 9600 bit/s, X.27 is
  required)
• X.21 mechanical characteristics are
• 15-pin connector per ISO Standard 4903

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CCITT X.21 Interface (Cont.)
4
Switched 64 kbit/s
X.21
DSU
Bridge
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CCITT X.21 Interface (Cont.)
Circuit Name Direction To DCE /
To DTE G Ground,Common Return Ga DTE Common
Return X Gb DCE Common Return X T Transmit
X R Receive X C Control
X I Indication X S Signal
Timing X B Byte Timing (Optional) X
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CCITT X.21 bis

• As an interim (perhaps longer term) provision, we
  have X.21 bis
• X.21 bis utilizes RS-232 for use with X.25
• Particularly used in countries where X.21 has not
  yet become available

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CCITT X.21 bis (Cont.)

• RS-232 signals are used to represent X.21 events
• To initiate the call
• Some X.21 features are not supported
• Call progress signals

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ISDN Interface
Terminal Equipment (TE)
Network Equipment (NE)
a
a
Power Source 3
b
b
c
c
d
d
Transmit
Transmit
Receive
e
Receive
e
f
f
g
Power Source 2
g
Power Sink2
h
h