Section 6 - Slide 1 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Modbus training Part 1 :Reference documents - WEB sites Part 2 :Definitions Part 3 : Modbus frame description Part 4 : Security of transmission Part 5 : Physical layer Part 6 : Main characteristics resume

Section 6 - Slide 2 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Modbus User guide Reference : TSX DG MOD * Detailed description of the Modbus protocol. X-WAY communication user guide Reference : TSX DR NET * This guide gives common characteristics to X-WAY Schneider networks. Communication application specific functions PL7 Micro/Junior/Pro Reference : TLX DS COM PL7 42 * Volume 1 : Common communication application Volume 2 : Modbus bus Part 1 : Reference documents - WEB sites Schneider documents

Section 6 - Slide 3 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 WEB sites Modbus.org : Modicon site for Modbus users. Transparent Factory : Schneider Electric site for Transparent Factory users. Modbus Plus : Modbus Plus Planning and installation. Part 1 : Reference documents - WEB sites

Section 6 - Slide 4 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Modbus protocol MODBUS Protocol is a messaging structure created by MODICON company to connect PLC to programming tools. It is now widely used to establish master-slave communication between intelligent devices. MODBUS is independent of the physical layer. It can be implemented using RS232, RS422, or RS485 or over a variety of media (e.g. fiber, radio, cellular, etc...). Part 2 : Définitions

Section 6 - Slide 5 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Modbus Serial line RS485 MODBUS Serial line RS485 is a low cost network using a master/slave medium access with a transmission speed from 1,200 to 115 Kbits/s. Application Presentation Session Transport Network Link Physical Master - Slave Modbus RS485-RS 232 Part 2 : Définitions

Section 6 - Slide 6 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Modbus TCP/IP MODBUS TCP/IP uses TCP/IP and Ethernet 10 Mbit/s or 100 Mbits/s to carry the MODBUS messaging structure. Application Préeentation Session Transport Network Link Physical CSMA / CD ETHERNET V2 ou Modbus TCP IP Part 2 : Définitions

Section 6 - Slide 7 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Modbus Plus MODBUS PLUS is a higher speed network 1 Mbit/s token passing derivative that uses the MODBUS messaging structure. Application Presentation Session Transport Network Link Physical Token passing Modbus RS485 Part 2 : Définitions

Section 6 - Slide 8 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Modbus ASCII and Modbus RTU The MODBUS protocol comes in 2 versions : ASCII transmission mode Each eight-bit byte in a message is sent as 2 ASCII characters. RTU transmission mode Each eight-bit byte in a message is sent as two four-bit hexadecimal characters. The main advantage of the RTU mode is that it achieves higher throughput. ASCII mode allows time intervals of up to 1 second to occur between characters without causing an error. Part 2 : Définitions

Section 6 - Slide 9 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Modbus frame structure AddressChecksumDataFunction The Modbus frame structure is the same for requests (master to slave messages) and responses (slave to master messages). Modbus ASCII Modbus RTU :CRLF 3A Hex 0D Hex 0A Hex Part 3 : Modbus frame description AddressChecksumDataFunction silence Silence >= 3,5 characters

Section 6 - Slide 10 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Address field AddressChecksumDataFunction Valid slave device addresses are in the range of decimal. The individual slave devices are assigned addresses in the range of Value 0 is reserved for broadcast messages (no response). Request : A master addresses a slave by placing the slave address in the address field of the message. Response : When the slave sends its response, it places its own address in this address field of the response to let the master know which slave is responding. Part 3 : Modbus frame description

Section 6 - Slide 11 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Valid codes are in the range of decimal. Request : The function code field tells the slave what kind of action to perform. Response : For a normal response, the slave simply echoes the original function code. For an exception response, the slave returns a code that is equivalent to the original function code with its most significant bit set to a logic 1. Function field AddressChecksumDataFunction Part 3 : Modbus frame description

Section 6 - Slide 12 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Valid codes are in the range of decimal. Request : The data field contains additional information which the slave must use to take the action defined by the function code. This can include items like register addresses, quantity of items to be handled, etc... Response : If no error occurs, the data field contains the data requested. If an error occurs, the field contains an exception code that the master application can use to determine the next action to be taken. Data field AddressChecksumDataFunction Part 3 : Modbus frame description

Section 6 - Slide 13 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Valid codes are in the range of decimal. Modbus RTU uses CRC : Cyclycal Reduncy Check (2 byte) Modbus ASCII uses LRC : Longitudinal Redundancy Check (1 bytes) Request : The checksum is calculated by the master and sends to the slave. Response : The checksum is re-calculated by the slave and compared to the value sent by the master. If a difference is detected, the slave will not construct a response to the master. Checksum field AddressChecksumDataFunction Part 3 : Modbus frame description

Section 6 - Slide 14 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Request : Frame exemple in RTU mode Function code = 03 : Read Holding Registers Slave Address CRC16 First word address Function code = 03 Number of words to read 1 byte 2 bytes Response : Slave Address CRC16 Number of bytes read Function code = 03 Value of the first word 1 byte 2 bytes Value of the last word 2 bytes Part 3 : Modbus frame description

Section 6 - Slide 15 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Request : Frame exemple in RTU mode Function code = 06 : Write Single Register Slave Address CRC16 Word address Function code = 06 Value of word 1 byte 2 bytes Response : Part 3 : Modbus frame description Slave Address CRC16 Word address Function code = 06 Value of word 1 byte 2 bytes

Section 6 - Slide 16 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Request : Frame exemple in RTU mode Function code = 16 (décimal) : Write Multiple Registers Slave Address CRC16 First word address Function code = 16 Number of words to write 1 byte 2 bytes Response : Slave Address CRC16 Function code = 16 1 byte 2 bytes Part 3 : Modbus frame description Value of the first word Number of bytes 1 byte2 bytes First word address Number of words to write

Section 6 - Slide 17 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Function code exemples Part 3 : Modbus frame description Code Function 01 (0x01)Read Coils 02 (0x02) Read Discrete Inputs 03 (0x03) Read Holding Registers 04 (0x04) Read Input Registers 05 (0x05) Write Single Coil 06 (0x06) Write Single Register 15 (0x0F) Write Multiple Coils 16 (0x10) Write Multiple Registers 23 (0x17)Read/Write Multiple Registers 43 (0x2B)Read Device Identification The complete description of all Modbus request is freely available on the Modbus.org web site :

Section 6 - Slide 18 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Parity checking Even or odd can be optionally applied to each character. Frame checking LRC or CRC is applied to the entire message. Continuous stream The entire message frame must be transmitted as a continuous stream. If a silent interval (more than 1.5 character times RTU mode or 1 second ASCII mode) occurs before completion of the frame, the receiving device flushes the incomplete message and assumes that the next byte will be the address field of a new message. Error checking methods Part 4 : Security of transmission

Section 6 - Slide 19 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 The master is configured by the user to wait for a predetermined timeout interval before aborting the transaction. This interval is set to be long enough for any slave to respond normally. If the slave detects a transmission error, the message will not be acted upon. The slave will not construct a response to the master. Thus the timeout will expire and allow the master's program to handle the error. Error checking methods Part 4 : Security of transmission

Section 6 - Slide 20 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 RS485 physical layer Part 5 : Physical layer RS485 is the most common physical layer used on Modbus. The RS485 standard allows variants of different characteristics : polarisation line terminator distribution of a reference potential number of slaves length of the bus

Section 6 - Slide 21 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 The various versions of the RS485 physical layer Part 5 : Physical layer The new Telemecanique devices conform to the Modbus specification published in 2002 on the Modbus.org web site. But some Schneider older devices comply with earlier specifications : Uni-Telway Jbus

Section 6 - Slide 22 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 New Modbus RS485 standard schematic Part 5 : Physical layer Master Slave 1Slave 2 D1 D0 Common 5 V 650  120  1 nF 120  1 nF

Section 6 - Slide 23 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Uni-Telway RS485 schematic Part 5 : Physical layer Master Slave 1Slave 2 D(B) D(A) 0 VL 5 V 4,7 K  120  1 nF 120  1 nF 4,7 K  5 V

Section 6 - Slide 24 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Jbus RS485 schematic Part 5 : Physical layer Master Slave 1 Slave 2 L-(B/B ’) L+(A/A ’) 5 V 470  150 

Section 6 - Slide 25 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Mixed RS485 schematic Part 5 : Physical layer Master Slave 1 Slave 2 D1 D0 Common 5 V Rp 120  1 nF 120  1 nF Rp 4,7 K  5 V Suitable polarization Rp must be calculated If the master is fitted with a 470  polarisation, it ’s possible to connect a maximum of 18 slaves with 4,7 K  polarisation

Section 6 - Slide 26 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Main characteristics resume Topology: Bus with line terminations Maximum distance:With RS485 : 1000 m without repeater Data rate: From 1,200 to 115 Kbits/s Max. no. of devices: With RS485 : 32 master included Part 6 : Main characteristics resume

Section 6 - Slide 27 / 27 P&T - GPS - Training PhW - 06_TECH_Modbus_en 06/ 2004 Method of accessing the medium: Master slave Transmission method: Messaging Max. useful data size: 120 words Transmission security: LRC or CRC Start and stop delimiters Parity bit Continuous stream Main characteristics resume Part 6 : Main characteristics resume