Download - Lecture 6 Serial Com Interface
Lecture 6 Serial Communication Intrerface
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Communication Interface
• RS-232/ RS-422/ RS-485• USB• GPIB
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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
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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
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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
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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)
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Voltage Level for EIA 232
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EIA 232 Transmitter and Receiver
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Common DB-9 and DB-25 Pin Assignment
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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
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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
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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
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RS-232 DB-25 Connectors
DB-25 Female
DB-25 Male
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RS-232 DB-9 Connectors
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RS-232C (signal)
Odd Parity
Even Parity
No Parity
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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
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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
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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.
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Typical Two Wire Multidrop Network
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Typical Four Wire Multidrop Network
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EIA 422/ 485 Receiver Sensitivities
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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
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Current Loop (4 to 20 mA)
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)
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Current Loop (4 to 20 mA)
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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
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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
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USB - Connectors
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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
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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)