ConceptConcept ofof SerialSerial CommunicationCommunication AgendaAgenda
Serial v.s. Parallel Simplex , Half Duplex , Full Duplex Communication RS-485 Advantage over RS-232 SerialSerial v.s.v.s. ParallelParallel Application: How to Measure the temperature in a long distance?
Measuring with a DAC card:
1200 m
Remote sensor Control room
T/C wire T/C A/D
noise Application: How to Measure the temperature in a long distance?
Measuring with a remote I/O module:
1200 m
Remote sensor Control room
T/C Remote I/O
Standard Serial Communication T/C signal, 4-20mA, 0-5V… Noise rejection (Differential signal) MostMost PopularPopular 33 typestypes ofof SerialSerial Comm.Comm.
z Most commonly available Tx Rx Rx Tx z Simple wiring CTS RTS z Low cost RTS CTS RS-232 z Short length (40 ft) DTR DSR DSR DTR Bar code reader z Slow data rates GND GND z Subject to noise
Tx+ z High data rates Tx- z Longer cable lengths (4000 ft) Rx+ Rx- RS-422 z Full-duplex GND z Noise rejection PLC
z Multipoint application (Up to 32 units) z Low cost Data+ z Longer cable lengths (4000 ft) Data- RS-485 zNoise immunity GND zHalf-duplex PLC SerialSerial V.S.V.S. ParallelParallel CommunicationCommunication Serial Communication Transfer the data bit by bit Synchronous Data Transfer
Bit
Send Data Receive Data Parallel Communication Transfer the all data simultaneously Asynchronous Data Transfer Bit Bit Bit Bit Bit Bit Bit Bit Send Data Receive Data SimplexSimplex ,, HalfHalf DuplexDuplex ,, FullFull DuplexDuplex CommunicationCommunication SimplexSimplex CommunicationCommunication
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 error or control signals to the transmit end. – The examples of simplex are broadcasting, or Radio
Simplex Channel Operation
One way only Half-DuplexHalf-Duplex CommunicationCommunication
Half 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
Half-Duplex Operation
Two way but not at the same time Full-DuplexFull-Duplex CommunicationCommunication
Full 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 Full-Duplex Operation
Both Way at the same time RS-485RS-485 AdvantageAdvantage overover RS-232RS-232 RS-232RS-232 CommunicationCommunication
Full-Duplex Operation No 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
Single-Ended Tx Single-Ended Driver Receiver
signal
Rx RS-232RS-232 PinPin AssignmentAssignment
Layouts and signals of DB25 and DB9 connector (RS-232)
25 pin 9 pin Signal Direction Description 1 - Shield - protection ground 13 25 2 3 TD DTE → DCE transmitted data 12 24 11 3 2 RD DCE → DTE received data 23 10 4 7 RTS DTE → DCE request to send 22 9 5 8 CTS DCE → DTE clear to send 5 21 9 8 6 6 DSR DCE → DTE data set ready 4 20 8 7 7 5 GND - signal ground (common) 3 19 7 6 2 18 8 1 DCD DCE → DTE data carrier detect 6 5 1 17 20 4 DTR DTE → DCE data terminal ready 4 16 22 9 RI DCE → DTE ring indicator 3 15 2 23 - DSRD DCE ↔ DTE data signal rate detector 14 1 DCE : Data Carrier Equipment (Modem) DTE : Data Terminal Equipment (PC’s COMport)
RS-232RS-232 Hand-ShakingHand-Shaking WiringWiring
Transfer Data with no handshaking Signal Pin Pin Signal TX 3 3 TX RX 2 2 RX GND 5 5 GND
Transfer Data with handshaking Signal Pin Pin Signal TX 3 3 TX RX 2 2 RX RTS 7 7 RTS CTS 8 8 CTS DSR 6 6 DSR CD 1 1 CD DTR 4 4 DTR GND 5 5 GND RS-232RS-232 ApplicationApplication
The Application for RS-232 1. PC’s and Laptops 2. Point of Sales Equipment (POS) 3. PDA’s and GPS’s 4. PC Peripherals (printers, faxes, mouse,…..) 5. Barcode Reader RS-485RS-485 CommunicationCommunication
Half-Duplex Operation Noise rejection and cross wire (Differential) Long transmission distance (Up to 1200m) High transmission speed (Up to 10Mbps ) Auto-Flow Control
Differential Differential Driver Twisted-pair Receiver
Signal Voltage
Twist Pair: to reduce the electromagnetic interference
VCM RS-485RS-485 CommunicationCommunication
Save the wiring cost Easy to setup and maintain Communication is more reliable
DATA+ (Y)
Host Rt Rt RS-485 DATA- (G)
Local Power Supply+ +Vs(R) - power +10 to +30 VDC GND(B) Y RGY supply GY
R G B RS-485RS-485 Multi-dropMulti-drop NetworkNetwork andand TerminationTermination
Terminal Resistor: To decrease the distortion of the signal
RT repeater RT
RX RX RX RX TX TX TX TX
Device 0 Device 31 Device 0 Device 31
32 driver / receiver 32 driver / receiver RS-485RS-485 ApplicationApplication
Typical RS-485 Applications 1. Point of Sales Equipment ( ex. Remote price checker,….) 2. Control System Automation (ex. PLC,….) 3. Power/Gas Meters
PLC Temperature AC Power Controller Monitor RS-422RS-422 CommunicationCommunication
The electrical spec. is similar to RS-485 protocol Key difference – 1 driver only can connect up to 10 receivers – Full-Duplex RS-422/485RS-422/485 PinPin AssignmentAssignment
Pin RS-422 RS-485 Pin RS-422 RS-485 1 TxD- Data- 2RxD+ 13 25 2 TxD+ Data+ 12 3 TxD+ Data+ 24 11 23 3RxD+ 10 4RTS+ 22 5 9 9 21 4 8 8 4RxD- 20 5CTS- 3 7 7 19 2 6 6 5GNDGND 18 6RTS- 1 5 17 4 6RTS- 16 7GNDGND 3 15 2 14 7RTS+ 1 8 TxD- Data- 8CTS+ 20 RxD- 9CTS- 22 CTS- RS-232RS-232 V.S.V.S. RS-422/485RS-422/485
Protocol 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 115.2Kbps 10Mbps 10Mbps Transfer Rate Transmission Full-Duplex Full-Duplex Half-Duplex Mode Point to Point Point to Point Multi-Drop QQ && AA Thanks~~~