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

Communication lines


Osi model

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 model1

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 model2

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 model3

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

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 eia2321

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

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

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

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

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 speed1

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

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

RS232 - Connectors

source: www.arcelect.com

9 pin


Rs232 connectors1

RS232 - Connectors

25 pin

source: fjkraan.home.xs4all.nl

source: www.solentcables.co.uk


Rs232 summary

RS232 - Summary

  • 1 transmitter, 1 receiver

  • Common ground

  • Typically 8 bit, no parity, 1 stop bit (8N1)


Rs 422 eia 422

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

Differential signaling

source: www.root.cz

source: www.root.cz


Rs 422

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

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

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

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


Communication lines

Half duplex

source: www.alciro.org


Communication lines

full duplex

source: www.alciro.org


Grounding

Grounding

source: hw.cz


Maximal speed

Maximal speed

source: hw.cz


Rs 422 vs rs 485

RS-422 vs. RS-485

source: hw.cz


Communication lines

USB

  • Universal serial bus (1995)

  • Differential signaling (DATA + , DATA -) + power

source: www.se7ensins.com

source: en.wikipedia.org


Usb specifications

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

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 signaling1

USB signaling

source: www.tek.com


Speed identification

Speed identification

  • Full speed device

source: www.beyondlogic.org


Speed identification1

Speed identification

  • Full speed device

source: www.beyondlogic.org


Non return to zero invert signaling

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 physical layer

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 physical layer1

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

Ethernet – Manchester encoding

  • Encoding helps clock recovery

source: en.wikipedia.org


Ethernet physical layer2

Ethernet – physicallayer

Ethernet data, showing MLT-3 encoding of bits. (used in e.g. 100BASE-TX)

source: flickr.com


Ethernet data link layer frame

Ethernet – Data Link Layer - frame

synchronization

source: communities.netapp.com


Ethernet data link layer frame1

Ethernet – Data Link Layer - frame

addresses

source: communities.netapp.com


Ethernet data link layer frame2

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 frame3

Ethernet – Data Link Layer - frame

data

source: communities.netapp.com


Ethernet data link layer frame4

Ethernet – Data Link Layer - frame

Control checksum

Cyclic redundancy check

source: communities.netapp.com


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