Communication lines
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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.

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Communication lines

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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

RX

TX

Log. 0 : > +3 V

Log. 1 : < -3 V

Log. 0 : +5 to +15 V

Log. 1 : -15 to -5 V

Noise immunity:

min. 2 V


RS232 (EIA232)

RX

TX

  • Length RS-232-C = 15 m

  • RS-232-F defines max. load capacity 2500 pF

signal

CRX

CS

CM

CS

~20 pF

shield


RS232 - Cable capacity

signal

CRX

CS

CS ~ 0,5 CM unshielded cable

CS ~ 2 CM shielded cable

CM

CS

~20 pF

shield

Max. length: Lmax = 2500 / Ctotal

Ctotal = CM + CS

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

data: 11010101b (213dec)

idle

  • Odd

  • Even

start

(parity)

0

0

0

0

1

1

1

1

1

1

stop

b0

idle

b2

b4

b6

b1

1,1.5,2

b3

b5

b7

LSB

MSB


RS232 - Asynchronous communication

Fixed comm. speed: tx + rx same (tolerance ~3%)

idle

RX

TX

start

(parity)

0

0

0

0

1

1

1

1

1

1

stop

b0

idle

b2

b4

b6

b1

b3

b5

b7


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 definesspeeds:

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

source: www.hw.cz


RS232 - Signals

RxD

TxD

Dev. 1

Dev. 2

RxD

TxD

RTS

CTS

Request to send

RTS

CTS

Clear to send

Data Carrier Detect

DTR

Data terminal ready

DCD

DSR

Data Set Ready

DCD

DSR

DTR

GND


RS232 - Connectors

source: www.arcelect.com

9 pin


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

Log. 0: VA – VB ≥ +0.2 V

Log. 1: VA – VB ≤ -0.2 V

source: www.scantec.de

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

Log. 0: VA – VB ≥ +0.2 V

Log. 1: VA – VB ≤ -0.2 V

Source: www.consultants-online.co.za

source: www.sealevel.com


RS-485 devices

Internally each node can have a transmitter and receiver, they are switched into high-impedance mode when not used

Source: www.root.cz


Half duplex

source: www.alciro.org


full duplex

source: www.alciro.org


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: www.se7ensins.com

source: 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

D+

device

host

D-

  • Differential „1“:

    D+ > 2.8 V, D- < 0.3V

  • Differential „0“:

    D-> 2.8 V, D+ < 0.3V

  • Differential „1“: D+ greaterthanD-

  • Differential „0“: D+ lessthanD-


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 Invertsignaling

  • "One" is represented by a transition of the physical level.

  • "Zero" has no transition.

source: www.jbmelectronics.com

source: en.wikipedia.org


Ethernet – physicallayer

  • 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 – physicallayer

Logic levels (10BaseT - output)

  • Log. 1 > +0.7 V

  • Log. 0< -0.7 V

source: hw-server.com

source: www.interfacebus.com

source: sigalrm.blogspot.com


Ethernet – Manchester encoding

  • Encoding helps clock recovery

source: en.wikipedia.org


Ethernet – physicallayer

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 checksum

Cyclic redundancy check

source: communities.netapp.com


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