Lecture 6 Serial Com Interface

Lecture 6 Serial Communication Intrerface

1

Communication Interface

• RS-232/ RS-422/ RS-485• USB• GPIB


2

Physical layer subdivision

mechanicalspecifications

electrical / opticalspecifications

medium-dependent signalling

medium-independent signallingsame for different media(e.g. coax, fibre, RS485)

applies to one media(e.g. optical fibres)

defines the mechanical interface(e.g. connector type and pin-out)

applies to one media type(e.g. 200µm optical fibres)

PhysicalLayer


3

Concept relevant to physical layer

Topology

Mechanical

Control Send, Receive, Collision

Interface Binary bit, Collision detection [multiple access]Signal quality supervision, redundancy control

Modulation

Binary, NRZ, Manchester,..

Synchronisation Bit, Character, Frame

Flow Control Handshake

Medium

Channels

Coding/Decoding

Baseband, Carrier band, Broadband

Ring, Bus, Point-to-point

Connector, Pin-out, Cable, Assembly

signals, transfer rate, levels

Half-duplex, full-duplex, broadcast


4

Generic Communication Interface Illustration

DTE DCE DCE DTE

Data Terminal Equipment

Data Communication Equipment

Data Terminal Equipment

Data Communication Equipment

Bit serial transmission lineSignal and control line

Signal and control line


5

RS-232

• EIA’s Recommended Standard (RS)• Specifies electrical, mechanical, functional and

procedural aspects of the interface• Point-to-point connection• Widely used for connection of DTEs and DCEs and

many other applications.• Specifies signaling between DTE and DCEs.• Uses NRZ-L encoding

– Voltage less than -3V = logic “1”– Voltage greater than +3V = logic “0”

• Rated for less than 20 kbps and distance shorter than 15 meter. (greater rate and distance is theoretically possible, but not necessary wise)


6

Voltage Level for EIA 232


7

EIA 232 Transmitter and Receiver


8

Common DB-9 and DB-25 Pin Assignment


9

Serial Port Handshake• Connecting PC to an access server via a pair of

modems• Control / Status Lines (two straight-through cables)

– Data Terminal Ready indicates that PC is on and ready

– Data Set Ready indicates that modem is on and ready

– With Request to Send, PC tells modem to turn on its carrier

– With Clear to Send, the modem indicates that carrier is on

– With Data Carrier Detect, the modem indicates carrier seen

– With Ring Indicator, modem indicates incoming call

PC Modem Modem

DTRDSRRTSCTSDCD

GND

DTRDSRRTSCTSDCD

GND

RemoteAccessServerTXD

RXDTXDRXD

Analog signalson phone line

RI RI


10

Serial Port Handshake• Connecting two PCs via a NULL modem cable

– Behaves like a pair of modems – Control / status lines are “cross-connected”– Transmit and receive data are “cross-connected”

TXDRXD

RTSCTSDCDGND

TXDRXD

RTSCTSDCDGND

DSR

(RI not normally needed)

DTRDSR

DTR


11

Serial Port Handshake• Bits are sent on TXD and RXD serially (one at a time)

– Bit Rate needs to be specified– When the sequence starts and stops has to be

specified– How the bits are serialized has to be specified

Arbitrary time sincelast character sent

One Start Bit One or Two Stop Bits

D0 D1 D2 D3 D4 D5 D6 D7

ASCII character sentWith LSB first in time

OptionalParity Bit

-12V

+12VBit value = 0

Bit value = 1

Bit Duration = 1 / Bit Rate


12

RS-232 DB-25 Connectors

DB-25 Female

DB-25 Male


13

RS-232 DB-9 Connectors


14

RS-232C (signal)

Odd Parity

Even Parity

No Parity


15

RS-485

• Serial link in differential mode between two or several (max 32) DTE and DCE.

• Characteristics:– Logic level 0 : 0 / +5 V– Logic level 1 : +5 / 0 V– Rate : 10 Mbps– Max number of station : 32– Maximum cable length : 1200 M


16

RS 485• The differential voltages on the A and B outputs of the driver

(transmitter) are similar (although not identical) to those for EIA-422, namely:

–1.5 V to –6 V on the A terminal with respect to the B terminal for a binary

1 (MARK or OFF) state, and

+1.5 V to +6 V on the A terminal with respect to the B terminal for a binary

0 (SPACE or ON state).• As with EIA-422, the line driver for the EIA-485 interface

produces a ±5 V differential voltage on two wires.• The major enhancement of EIA-485 is that a line driver can

operate in three states called tri-state operation:

Logic 1

Logic 0

High-impedance


17

RS-485

DTE_1

T

R

DCE_1

ctrl

+

+ +

+

+

+

+

+

R

R

R

DCE_2

DTE_2

T

T

T

ctrl

ctrl

ctrl

Example: multipoint connection in half-duplex mode.


18

Typical Two Wire Multidrop Network


19

Typical Four Wire Multidrop Network


20

EIA 422/ 485 Receiver Sensitivities


21

Current Loop (4 to 20 mA)

• Serial connection between 2 or several (max 16) DTE and DCE.

• Characteristics:– Logic level 0 : I ≤ 4 mA

– Logic level 1 : 15 ≤ I ≤ 20 mA

– Rate : 20 Kbps– Max number of station : 16– Maximum cable length : 3700 M


22


T

R

I1

I2 T R

DTE_1(sensor)

DTE_2(PLC)

Example : Point –to-point connection in half duplex mode. ( usually use for connection of sensors and PLC in a noisy environement)


23



24

USB-Universal Serial Bus• Widely use in PC.• USB enable “plug and play” connection to

several computer peripherals.– Human-Computer interface

• Mouse, keyboard, joystick, bar code reader etc

– Data storage devices• Hard disks, DC ROM

– Display unit• Monitor, printer, scanner, digital camera

– Communication device • Modem


25

USB

• Peripheral without USB port such as PLC, microcontroller can be connected to a USB port at a PC through an adapter:– USB ↔ RS-232/ RS-485– USB ↔ IEEE 488/ Centronics– USB ↔ Internet interface 10BaseT-

100BaseTx


26

USB - Connectors


27

USB - Connectors• Each connector has four leads

– 2 leads for data (D+ and D -)– 2 leads for supply (Vbus and ground)

The wire comprise 2 twisted pair with metallic shield and its maximum length is 5 meters.

VBUS

GND

D +D -

Lead No Signal Color 1 VBUS (+5 V) Red 2 D - White 3 D + Green 4 GND Black


28

USB – transmission rate

• USB High speed = 480 Mbps (USB version 2.0)• USB Full speed = 12 Mbps (USB version

1.0)• USB Low speed = 1,5 Mbps (versions 1 ou 2)

Lecture 6 Serial Com Interface

Documents

Transcript of Lecture 6 Serial Com Interface