communication lines. osi model open systems interconnection (osi) model (iso/iec 7498-1) source:...
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Communication lines
OSI model
• Open Systems Interconnection (OSI) model (ISO/IEC 7498-1)
Source: homepages.uel.ac.uk
• Physical layer – specifies electrical and physical properties (cable)
• Pins, voltages, impedance, modulation, timing, topology
OSI model
• Open Systems Interconnection (OSI) model (ISO/IEC 7498-1)
Source: homepages.uel.ac.uk
• Physical layer – Transmits raw bit stream over physical cable
• IEEE 802, RS232, RS422, RS485, I2C, SPI,…
OSI model
• Open Systems Interconnection (OSI) model (ISO/IEC 7498-1)
Source: homepages.uel.ac.uk
• Data link layer – specifies network data frame (packet), checksum, source and destination address, and data
• E.g. Ethernet MAC, RS232
OSI model
• Open Systems Interconnection (OSI) model (ISO/IEC 7498-1)
Source: homepages.uel.ac.uk
• Network layer – routing, directing datagrams from one network to another
• E.g. IP addresses
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 RX
Log. 0 : +5 to +15 VLog. 1 : -15 to -5 V
Log. 0 : > +3 VLog. 1 : < -3 VNoise immunity:
min. 2 V
RS232 (EIA232)
• Length RS-232-C = 15 m• RS-232-F defines max. load capacity 2500 pF
TX RX
CRX
~20 pF
CM
signal
shield
CS
CS
RS232 - Cable capacity
CS ~ 0,5 CM unshielded cable
CS ~ 2 CM shielded cable
CRX
~20 pF
CM
signal
shield
CS
CS
Max. length: Lmax = 2500 / Ctotal
Ctotal = CM + CS
e.g. Belden 1700A TP: 78,7 Ω/km, 45,9 pF/m
RS232 - Communication protocol
idle
Log. 0 : +5 to +15 VLog. 1 : -15 to -5 V
start
0
1
0
1
0
1
0
1 1
b0b1
b2b3
b4b5
b6b7
stop idle
1
(parity)• Odd• Even
data: 11010101b (213dec)
LSB MSB
1,1.5,2
RS232 - Asynchronous communication
idle
Fixed comm. speed: tx + rx same (tolerance ~3%)
start
0
1
0
1
0
1
0
1 1
b0b1
b2b3
b4b5
b6b7
stop idle
1
(parity)
TX RX
RS232 - Communication speedRS-232-F limits to 30 V/µs, max 4% of bit time => max. theoretical speed 200 kbit/s 0
11
Δt
ΔV
RS232 - Communication speedRS-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
RS232 - SignalsDev. 1 Dev. 2
TxD
RxD
GND
RxD
TxD
RTS Request to send
CTS Clear to send
CTS
RTS
DTR Data terminal ready DCDData Carrier Detect
DSRData Set Ready
DTRDSR
DCD
RS232 - Connectors
source: fjkraan.home.xs4all.nl
25 pin
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: meteosat.pessac.free.fr
source: www.scantec.de
Log. 0: VA – VB ≥ +0.2 V
Log. 1: VA – VB ≤ -0.2 V
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
source: www.sealevel.com
Log. 0: VA – VB ≥ +0.2 V
Log. 1: VA – VB ≤ -0.2 V
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.orgHalf duplex
source: www.alciro.orgfull duplex
USB• Universal serial bus (1995)
• Differential signaling (DATA + , DATA -) + power
source: www.se7ensins.comsource: en.wikipedia.org
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
host device
• Differential „1“: D+ greater than D-
• Differential „0“: D+ less than D-
D+
D-
• Differential „1“: D+ > 2.8 V, D- < 0.3V• Differential „0“:D- > 2.8 V, D+ < 0.3V
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+, RX-
source: techpubs.sgi.com
Ethernet – physical layer
Logic levels (10BaseT - output)• Log. 1 > +0.7 V• Log. 0 < -0.7 V
source: hw-server.com
source: sigalrm.blogspot.comsource: www.interfacebus.com
Ethernet – Manchester encoding
source: en.wikipedia.org
• Encoding helps clock recovery
Ethernet – physical layer
Ethernet data, showing MLT-3 encoding of bits. (used in e.g. 100BASE-TX)
source: flickr.com
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 checksumCyclic redundancy check
source: communities.netapp.com