1. Networking A method of exchanging data between two physically distant nodes. Two devices are said to be networked when a process in one device is able to exchange information with a process in another device.

2. Why Network? Why network a PLC control system? Less wire and complexity in construction Two way communications Longer distances Multiple Systems supervised by “controller”

3. HART Protocol Highway Addressable Remote Transducer Communicates over 4-20mA current loops Modulates the digital signal on top of the analogue current signal in the loop Early implementation of Fieldbus

4. HART Protocol cont.

5. Frequency Modulation carrier signal

6. Serial Communications RS 232  Point to Point Protocol  Low line speed (baud rate)  Short Distances ~ 100m  Still use for programming the PLCs

7. Serial Communications RS 422  Point to Point Protocol and  Multi-drop. 1 Master & 10 receivers  Greater Distances ~ 1500m  Common use is for RS-232 extenders

8. Serial Communications RS 485  Point to Point, Multi Drop and Multi Point  Up to 32 devices  Uses Differential signalling  Greater Distances ~ 1200m  Only requires 2 wires and configured as a bus

9. Modbus Developed by Schneider Electric in the late 70’s Has become the de facto standard Has been “open sourced” in that it is openly published and royalty fee

10. Modbus Can link up to 250 devices on a RS-485 cable Can be encapsulated inside other protocols (Ethernet) with the use of protocol convertors (blackbox convertors) or Modbus TCP frame format Serial based on Master/Slave operation. Ethernet more like a peer-to-peer network

11. Modbus Client/Server communication on an Ethernet Network MODBUS Request is the message sent on the network by the client to initiate a transaction MODBUS Indication is the request message received on the server side MODBUS Response is the response message sent by the server MODBUS Confirmation is the response message received on the client side

12. Modbus The Modbus messaging services (client/server model) are used for real time information exchange Between two device applications Between device applications and other devices Between HMI/SCADA applications and devices Between PC and device providing online services

13. Modbus Typical Modbus network with multiple clients/servers

14. Modbus Defines simple Protocol Data Unit (PDU) and application Data Unit (ADU)

15. EtherCAT Open high performance Ethernet-based fieldbus system. Founded in 2003 Germany Uses “standard” Ethernet for the interexchange of data Synchronization with distributed clock Works as a “peer to peer” network

16. Fieldbus Standardised as IEC 61158 Multiple topologies and protocols (types): Star, Ring, Daisy-chain Type 1 Foundation Fieldbus H1 Type 2 ControlNet Type 3 PROFIBUS Type 4 P-Net Type 5 FOUNDATION fieldbus HSE (High Speed Ethernet) Type 6 SwiftNet (a protocol developed for Boeing, since withdrawn) Type 7 WorldFIP Type 8 Interbus http://en.wikipedia.org/wiki/List_of_automation_protocols

17. More on Protocols Open vs. closed protocols and standards Advantages and disadvantages: Time taken to develop Cost per license Adoption rate Ability to change and grow

18. More Modern Protocols Why the need?  Each transducer requires a discrete input (unless TDMA multiplexing)  Distance between controller and transducer only up to ~1500m  More information required than just 1 output allows  More wiring required for each transducer.

19. OSI Model TCP/IP Transfer Control Protocol Internet Protocol Includes TCP and UDP Requires the use of “ports”

20. OSI model Data unit LayerFunction Host layers Data 7. ApplicationApplicationNetwork process to application 6. PresentationPresentation Data representation, encryption and decryption, convert machine dependent data to machine independent data 5. SessionSession Interhost communication, managing sessions between applications Segments4. TransportTransportEnd-to-end connections, reliability and flow controlflow control Media layers PacketPacket/DatagramDatagram3. NetworkNetworkPath determination and logical addressinglogical addressing Frame2. Data linkData linkPhysical addressing Bit1. PhysicalPhysicalMedia, signal and binary transmission

21. Lab Work Connect two laptops up with Null-modem cable, use a terminal emulator program (putty) and configure for serial communications. Try settings baud rate to 100 and note speed. Then connect one laptop to oscilloscope, and observe the various voltages and time scales.

22. LetterASCII CodeBinaryLetterASCII CodeBinary a09701100001A06501000001 b09801100010B06601000010 c09901100011C06701000011 d10001100100D06801000100 e10101100101E06901000101 f10201100110F07001000110 g10301100111G07101000111 h10401101000H07201001000 i10501101001I07301001001 j10601101010J07401001010 k10701101011K07501001011 l10801101100L07601001100 m10901101101M07701001101 n11001101110N07801001110 o11101101111O07901001111 p11201110000P08001010000 q11301110001Q08101010001 r11401110010R08201010010 s11501110011S08301010011 t11601110100T08401010100 u11701110101U08501010101 v11801110110V08601010110 w11901110111W08701010111 x12001111000X08801011000 y12101111001Y08901011001 z12201111010Z09001011010