Download Communication lines

Communication lines
OSI model
• Open Systems Interconnection (OSI) model
(ISO/IEC 7498-1)
• Physical layer –
specifies electrical
and physical
properties (cable)
• Pins, voltages,
impedance,
modulation, timing,
topology
Source: homepages.uel.ac.uk
OSI model
• Open Systems Interconnection (OSI) model
(ISO/IEC 7498-1)
• Physical layer –
Transmits raw bit
stream over physical
cable
• IEEE 802, RS232,
RS422, RS485, I2C,
SPI,…
Source: homepages.uel.ac.uk
OSI model
• Open Systems Interconnection (OSI) model
(ISO/IEC 7498-1)
• Data link layer –
specifies network
data frame (packet),
checksum, source
and destination
address, and data
• E.g. Ethernet MAC,
RS232
Source: homepages.uel.ac.uk
OSI model
• Open Systems Interconnection (OSI) model
(ISO/IEC 7498-1)
• Network layer –
routing, directing
datagrams from one
network to another
• E.g. IP addresses
Source: homepages.uel.ac.uk
RS232 (EIA232)
•
•
•
•
Dates from 1969 (RS-232-C)
Last standard is TIA/EIA-232-F from 1997
Defines physical and data link layer
Single transmitter and receiver
TX
Log. 0 : +5 to +15 V
Log. 1 : -15 to -5 V
RX
Noise immunity:
min. 2 V
Log. 0 : > +3 V
Log. 1 : < -3 V
RS232 (EIA232)
TX
RX
• Length RS-232-C = 15 m
• RS-232-F defines max. load capacity 2500 pF
signal
CS
CS
shield
CM
CRX
~20 pF
RS232 - Cable capacity
signal
CS
CS
CM
CRX
~20 pF
shield
Max. length: Lmax = 2500 / Ctotal
Ctotal = CM + CS
CS ~ 0,5 CM unshielded cable
CS ~ 2 CM shielded cable
e.g. Belden 1700A TP: 78,7 Ω/km, 45,9 pF/m
RS232 - Communication protocol
Log. 0 : +5 to +15 V
Log. 1 : -15 to -5 V
start
0
idle
0
data: 11010101b (213dec)
• Odd
(parity)
• Even
0
0
1
1
1
b0
b2
b4
b1
LSB
b3
1 1
b5
b6
1
stop
1,1.5,2
b7
MSB
idle
RS232 - Asynchronous communication
Fixed comm. speed: tx + rx same (tolerance ~3%)
TX
RX
start
(parity)
0
idle
0
0
0
1
1
1
b0
b2
b4
b1
b3
1 1
b5
b6
b7
1
stop
idle
RS232 - Communication speed
RS-232-F limits to 30 V/µs, max 4% of bit time => max.
theoretical speed 200 kbit/s 0
ΔV
1
1
Δt
RS232 - Communication speed
RS-232-F standard defines speeds:
50,75,110,150,300,600,1200,2400,4800,9600,19200 bit/s
Common speeds above standard definition:
28800, 38400, 57600, 115200 bit/s
Higher speed
= lower distance
Baud rate [Bd]
Max length [ft]
Max length [m]
19 200
50
15
9 600
500
150
4 800
1 000
300
2 400
3 000
900
source: www.hw.cz
Dev. 1
TxD
RS232 - Signals
RxD
RxD
TxD
RTS
Request to send
CTS
CTS
Clear to send
RTS
DTR
DCD
Data terminal ready
Data Carrier Detect
Data Set Ready
DSR
DCD
DSR
DTR
GND
Dev. 2
RS232 - Connectors
9 pin
source: www.arcelect.com
RS232 - Connectors 25 pin
source: fjkraan.home.xs4all.nl
source: www.solentcables.co.uk
RS232 - Summary
• 1 transmitter, 1 receiver
• Common ground
• Typically 8 bit, no parity, 1 stop bit (8N1)
RS-422 (EIA-422)
• ANSI/TIA/EIA-422-B or ITU-T
Recommendation T-REC-V.11
•
•
•
•
•
Uses differential signaling + GND
1 transmitter + 10 receivers
10 Mbit/s (12 m), 100 kbit/s (1200 m)
Max. 1200 m
Standard does not define protocol and pins
Differential signaling
source: www.root.cz
source: www.root.cz
RS-422
source: www.scantec.de
Log. 0: VA – VB ≥ +0.2 V
Log. 1: VA – VB ≤ -0.2 V
source: meteosat.pessac.free.fr
RS-485
• ANSI/TIA/EIA-485 (1998)
•
•
•
•
Uses differential signaling
32 transmitter + 32 receivers
10 Mbit/s (12 m), 100 kbit/s (1200 m)
Max. 1200 m
• Standard does not define protocol and pins
RS-485 signaling
Source: www.consultants-online.co.za
Log. 0: VA – VB ≥ +0.2 V
Log. 1: VA – VB ≤ -0.2 V
source: www.sealevel.com
RS-485 devices
Source: www.root.cz
Internally each node can have a transmitter and
receiver, they are switched into high-impedance
mode when not used
source: www.alciro.org
Half duplex
source: www.alciro.org
full duplex
Grounding
source: hw.cz
Maximal speed
source: hw.cz
RS-422 vs. RS-485
source: hw.cz
USB
• Universal serial bus (1995)
• Differential signaling (DATA + , DATA -) + power
source: en.wikipedia.org
source: www.se7ensins.com
USB specifications
•
•
•
•
•
Max. 127 devices
Superspeed – 5 Gbit/s (USB 3.0 - 2008)
High Speed - 480Mbits/s (USB 2.0 - 1999)
Full Speed - 12Mbits/s
Low Speed - 1.5Mbits/s
USB signaling
• Uses NRZI (Non Return to Zero Invert) signaling
D+
host
D-
• Differential „1“:
D+ > 2.8 V, D- < 0.3V
• Differential „0“:
D- > 2.8 V, D+ < 0.3V
device
• Differential „1“:
D+ greater than D• Differential „0“:
D+ less than D-
USB signaling
source: www.tek.com
Speed identification
• Full speed device
source: www.beyondlogic.org
Speed identification
• Full speed device
source: www.beyondlogic.org
Non Return to Zero Invert signaling
• "One" is represented by a transition of the
physical level.
• "Zero" has no transition.
source: en.wikipedia.org
source: www.jbmelectronics.com
Ethernet – physical layer
• Standard IEEE 802.3
• Max. length 100m
• 3 Mbit/s to 100 Gbit/s
• Differential signaling
• Signals TX+, TX-, RX+, RXsource: techpubs.sgi.com
Ethernet – physical layer
source: hw-server.com
Logic levels (10BaseT - output)
• Log. 1 > +0.7 V
• Log. 0 < -0.7 V
source: www.interfacebus.com
source: sigalrm.blogspot.com
Ethernet – Manchester encoding
• Encoding helps clock recovery
source: en.wikipedia.org
Ethernet – physical layer
source: flickr.com
Ethernet data, showing MLT-3 encoding of
bits. (used in e.g. 100BASE-TX)
Ethernet – Data Link Layer - frame
synchronization
source: communities.netapp.com
Ethernet – Data Link Layer - frame
addresses
source: communities.netapp.com
Ethernet – Data Link Layer - frame
identifies what higher-level
network protocol is being carried
in the frame (example: TCP/IP)
source: communities.netapp.com
Ethernet – Data Link Layer - frame
data
source: communities.netapp.com
Ethernet – Data Link Layer - frame
Control checksum
Cyclic redundancy check
source: communities.netapp.com