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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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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


Half duplex

source: www.alciro.org


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


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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