ANALOG AND DIGITAL PHYSICAL INTERFACES Habib Youssef, Ph.D [email protected] Department of Computer Engineering King Fahd University of Petroleum and Minerals Dhahran, Saudi Arabia COMPUTER NETWORK
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ANALOG AND DIGITAL PHYSICAL INTERFACES
Habib Youssef, Ph.D
[email protected] of Computer Engineering King Fahd University of Petroleum and
MineralsDhahran, Saudi Arabia
COMPUTER NETWORK
The RS-232/CCITT V.24 and V.28 Interface
Data
Out of Band
Control
Computer
DTEDCE
Modem
Data
Out of Band
Control
DCEDTE
Computer
Modem
RS-232/CCITT V.24
DTE : Data Terminal Equipment
DCE : Data Circuit Termination Equipment
Data processing (DTE) to modem (DCE) interface
The CCITT V.24 Recommendation defines the interchange circuits» V.28 defines the electrical characteristics
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)
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
The RS-232/CCITT V.24 and V.28 Interface (Cont.)
The RS-232/CCITT V.24 and V.28 With Null
Modems
2
3
4
5
6
8
20
7
2
3
4
5
6
8
20
7
Data
Data
Req to Send
Clear to Send
Data Set Ready
Signal Detect
Data Terminal Ready
Req to SendClear to Send
Data Set Ready
Signal Detect
Data Terminal Ready
Data
Data
Signal Ground
Note : There are many variations to Null Modem Cross Connection
DCEDTE Null Modem
Pin Assignments for V.24/EIA-232
14 15 2116 2017 1918 22 23 24 25
1 2 3 4 5 6 7 8 9 10 11 12 13
Shield
Tx Data
Rx Data
Reg to Send
Clear to Send
DCE Ready
GND
Carrier Detect
Reserved for testing
Reserved for testing
Unassigned
Secn. Recv. Line Signal
Detector
Secn. CTS
Secondary Tx Data
Transmitter signal element
timing
Secondary received data
Transmitter signal element
timingLocal
Loopback
Secondary RTS
DTE Ready
Remote Loopback
Ring Indicator
Data Signal Rate Select
Transmit signal element
timing
Test Mode
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
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
RS-232/CCITT V.24 & V.28 Related Products (Cont.)
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
The Evolution of RS-232-C
RS-232-C
EIA-232-D (1987)• Unbalanced circuits
RS-530 (1987)•Balanced Circuits
V.35•Balanced Circuits
RS-449 signalsRS-422/423 electrical (1977)RS-442 balanced circuitsRS-443 unbalanced circuits
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
Start
End
10
Characters
V.24/EIA-232 dial-up operation
RS-423/CCITT V.10Single Ended Interchange
Circuit
Signal return
Trans Recvr
ErrorNoise
Note: V.10 is the same as X.26 or RS-423-A (unbalanced)
RS-422/CCITT V.11 Differential Interchange
Circuit
Trans Recvr
Noise Sensitive to differential
signal
Termination resistor
Noise was rejected
Note : V.11 is the same as X.27 or RS-422-A (balanced)
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
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
CCITT X.21 Interface (Cont.)
X.21
Switched 64 kbit/s
DSU Bridge
4
CCITT X.21 Interface (Cont.)
Circuit Name DirectionTo DCE / To DTE
G Ground,Common ReturnGa DTE Common Return XGb DCE Common Return XT Transmit XR Receive XC Control XI Indication XS Signal Timing XB Byte Timing (Optional) X
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
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
ISDN Interface
Power Source 3
Transmit
Receive
Power Source 2
Terminal Equipment (TE)
a
b
c
d
e
f
g
h
a
b
c
d
e
f
g
h
Transmit
Receive
Power Sink2
Network Equipment (NE)
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