Concept of Serial Communication
Concept of Serial Communication
AgendaAgenda
Serial v.s. ParallelSimplex , Half Duplex , Full Duplex CommunicationRS-485 Advantage over RS-232
Serial v.s. ParallelSerial v.s. Parallel
Application: How to Measure the temperature in a long distance?
Remote sensor
T/C
Control room
A/DT/C wire
noise
1200 m
Measuring with a DAC card:
Application: How to Measure the temperature in a long distance?
Measuring with a remote I/O module:
Remote sensor
T/C
Control room
Remote I/O
Noise rejection (Differential signal)
Standard T/C signal,
4-20mA,0-5V…
Serial Communication
1200 m
Most Popular 3 types of Serial Comm.Most Popular 3 types of Serial Comm.
TxTxRxRx
CTSCTSRTSRTSDTRDTRDSRDSRGNDGND
RxRxTxTx
RTSRTSCTSCTSDSRDSRDTRDTRGNDGND
TxTx++TxTx--
Rx+Rx+RxRx--
GNDGND
Data+Data+
DataData--
GNDGND
RSRS--232232
RSRS--422422
RSRS--485485
Most commonly availableSimple wiringLow costShort length (40 ft)Slow data ratesSubject to noise
High data ratesLonger cable lengths (4000 ft)Full-duplexNoise rejection
Multipoint application (Up to 32 units)Low costLonger cable lengths (4000 ft)
Noise immunityHalf-duplex
Bar code readerBar code reader
PLCPLC
PLCPLC
Serial V.S. Parallel CommunicationSerial V.S. Parallel CommunicationSerial CommunicationTransfer the data bit by bitSynchronous Data Transfer
Parallel CommunicationTransfer the all data simultaneouslyAsynchronous Data Transfer
Send Data Receive Data
BitBitBitBitBitBitBitBit
BitBitBitBitBitBitBitBit
Receive DataSend Data
Simplex , Half Duplex , Full Duplex Communication
Simplex , Half Duplex , Full Duplex Communication
Simplex CommunicationSimplex Communication
Simplex Communication :– Data in a simplex channel is always one way. Simplex channels
are not often used because it is not possible to send back erroror control signals to the transmit end.
– The examples of simplex are broadcasting, or Radio
One way only
Simplex Channel OperationSimplex Channel Operation
Half-Duplex CommunicationHalf-Duplex CommunicationHalf Duplex Communication :
– A half-duplex channel can send and receive, but not at the same time. It's like a one-lane bridge where two way traffic must give way in order to cross. Only one end transmits at a time, the other end receives.
– Another examples of half-duplex are talk-back radio , RS-485
Two way but not at the same time
HalfHalf--Duplex OperationDuplex Operation
Full-Duplex CommunicationFull-Duplex CommunicationFull Duplex Communication
– Data can travel in both directions simultaneously. There is no need to switch from transmit to receive mode like in half duplex. Its like a two lane bridge on a two-lane highway. Have you ever watched these television talk shows where the host has a number of people on the show, and they all try to talk at once. Well, that‘s full duplex!
– All examples of full-duplex are RS-232, RS-422, telephone
Both Way at the same time
FullFull--Duplex OperationDuplex Operation
RS-485 Advantage over RS-232RS-485 Advantage over RS-232
RS-232 CommunicationRS-232 CommunicationFull-Duplex OperationNo noise rejection (single-ended)Short transmission distance (within 15m)Low transmission speed (within 115.2kbps)Protocol
1. Point-to-point : Handle communication between 2 devices.2. Unbalanced lines (Single-ended.) : Signal applied to one line and referenced to ground.3. Most common use as a communication device for a Serial port of the PC and peripherals
signal
Single-EndedDriver
Single-EndedReceiver
Tx
Rx
RS-232 Pin AssignmentRS-232 Pin Assignment
Layouts and signals of DB25 and DB9 connector Layouts and signals of DB25 and DB9 connector (RS(RS--232)232)
25 pin 9 pin Signal Direction Description 1 - Shield - protection ground 2 3 TD DTE → DCE transmitted data 3 2 RD DCE → DTE received data 4 7 RTS DTE → DCE request to send 5 8 CTS DCE → DTE clear to send 6 6 DSR DCE → DTE data set ready 7 5 GND - signal ground (common) 8 1 DCD DCE → DTE data carrier detect 20 4 DTR DTE → DCE data terminal ready 22 9 RI DCE → DTE ring indicator 23 - DSRD DCE ↔ DTE data signal rate detector
DCE : Data Carrier Equipment (Modem) DTE : Data Terminal Equipment (PC’s COMport)
9
8
7
6
5
4
3
2
1
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
RS-232 Hand-Shaking WiringRS-232 Hand-Shaking WiringTransfer Data with no handshaking
Signal Pin
TXRX
GND
325
SignalPin
TXRX
GND
325
Signal Pin
TXRXRTSCTSDSRCD
DTRGND
32786145
SignalPin
TXRXRTSCTSDSRCD
DTRGND
32786145
Transfer Data with handshaking
RS-232 ApplicationRS-232 Application
The Application for RS-2321. PC’s and Laptops2. Point of Sales Equipment (POS)3. PDA’s and GPS’s4. PC Peripherals (printers, faxes, mouse,…..)5. Barcode Reader
RS-485 CommunicationRS-485 Communication
Half-Duplex OperationNoise rejection and cross wire (Differential)Long transmission distance (Up to 1200m)High transmission speed (Up to 10Mbps )Auto-Flow Control
DifferentialDriver
DifferentialReceiver
SignalVoltage
Twisted-pair
VCM
Twist Pair: to reduce the electromagnetic interference
RS-485 CommunicationRS-485 Communication
Save the wiring costEasy to setup and maintainCommunication is more reliable
BR G
Y RGY GY
HostRS-485
Power Supply+10 to +30 VDC
DATA+ (Y)
+Vs(R)
GND(B)
DATA- (G)Rt Rt
Local power supply
+-
RS-485 Multi-drop Network and TerminationRS-485 Multi-drop Network and Termination
RXTX
RXTX
repeater
RXTX
RXTX
Device 0 Device 31 Device 0 Device 31
32 driver / receiver
RT RT
32 driver / receiver
Terminal Resistor: To decrease the distortion of the signal
RS-485 ApplicationRS-485 Application
Typical RS-485 Applications1. Point of Sales Equipment ( ex. Remote price checker,….)2. Control System Automation (ex. PLC,….)3. Power/Gas Meters
PLC Temperature Controller
AC Power Monitor
RS-422 CommunicationRS-422 CommunicationThe electrical spec. is similar to RS-485 protocolKey difference
– 1 driver only can connect up to 10 receivers– Full-Duplex
RS-422/485 Pin AssignmentRS-422/485 Pin Assignment
Pin RS-422 RS-485
1 TxD- Data-
2 TxD+ Data+
3 RxD+
4 RxD-
5 GND GND
6 RTS-
7 RTS+
8 CTS+
9 CTS-
9
8
7
6
5
4
3
2
1
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Pin RS-422 RS-485
2 RxD+
3 TxD+ Data+
4 RTS+
5 CTS-
6 RTS-
7 GND GND
8 TxD- Data-
20 RxD-
22 CTS-
RS-232 V.S. RS-422/485RS-232 V.S. RS-422/485Protocol RS-232 RS-422 RS-485
Signal Single-Ended Differential Differential
Driving No. 1 10 32
Receiving No. 1 10 32
Distance 15m 1200m 1200m
Max. Data Transfer Rate
115.2Kbps 10Mbps 10Mbps
Transmission Mode
Full-DuplexPoint to Point
Full-DuplexPoint to Point
Half-DuplexMulti-Drop
Q & AQ & A
Thanks~~~
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