Getting Started with Modbus TCP/IP for AC Tech Drives

Transcription

1 Contained herein is the basic information for setting up AC Tech SMV Inverter and PositionServo drives for Modbus TCP/IP communication. For detailed information on the Modbus option module, refer to the product's Modbus Communications Reference Guide (SMV: CMVMB401, PositionServo: P94MOD01). Topics discussed in this application note include cabling, framing, switches and hubs, addressing, subnet masking and register numbering. For Further Reference Getting Started with Modbus TCP/IP for AC Tech Drives Modbus-IDA: AC Tech Library: Common Terms CIP TM Ethernet Modbus Ping Protocol TCP/IP Common Industrial Protocol Hardware and data transport medium for Modbus TCP/IP Open fieldbus standard for a multi-drop network based on master/client architecture Request information from a node Set of rules about communication on a network. Rules on: syntax (data format); semantics (interpretation of data); timing (transmission agreement between sender and receiver) Transmission Control Protocol / Internet Protocol Ethernet: In this application, Ethernet refers to a hardware and data transport medium. It does not specify a COM protocol. Modbus TCP/IP (MB TCP/IP) is a specific protocol implemented over an Ethernet network. Cabling: For new installations use at least Cat 5e rated cable. Cat 6 cable can also be used and offers better attenuation, but is more costly. Some installations may require plenum rated cable per building code. Plenum rated cabling has different insulation materials that do not smoke. As such they are required in air passageways, such as above ceiling tiles. Consult your local building code for required cabling. How to make up cables: Two types of cables are required for Ethernet networks: patch (straight through) cables and cross-over cables. Patch cables are used to connect devices to either hubs or switches. Cross-over cables can be used to connect two devices (such as a 940 Position Servo and a PC) directly together. T568B is the current convention used to color code Ethernet cabling. The RJ45 pinout is illustrated in Figure Figure 1: RJ45 Pin Diagram Table 1: Patch Cable (straight through wiring - both ends the same) RJ45 Pin# Wire Color RJ45 Pin# Wire Color 1 White/Orange 5 White/Blue 2 Orange 6 Green 3 White/Green 7 White/Brown 4 Blue 8 Brown AN 0024/A1 June 2007

2 Table 2: Cross-Over Cable RJ45 Pin# (End 1) Wire Color (End 1) RJ45 Pin# (End 2) Wire Color (End 2) 1 White/Orange 1 White/Green 2 Orange 2 Green 3 White/Green 3 White/Orange 4 Blue 4 White/Brown 5 White/Blue 5 Brown 6 Green 6 Orange 7 White/Brown 7 Blue 8 Brown 8 White/Blue Maximum Cable Length: On a 100 Base-T network segment the maximum between the two communicating nodes is 100 meters. This is due to timing constraints and fault detection. A network segment is a group of nodes on a Ethernet network which can all see ALL network traffic directed both to themselves and any other node. This is known as the domain of collision. If for example you had a PLC and an SMVector drive connected to different ports on a hub, the sum of the lengths of both patch cables added together must be less than 100 meters as illustrated in Figure 2. Under no circumstance can a network cable be longer than 100 meters in a 100 base-t network. Modbus TCP/IP 100 BASE-T Network Segment NODE NODE NODE Hub Drive PLC Figure 2: Maximum Cable Length Switches vs. Hubs: Hubs act basically as a dumb repeater. They repeat any message from any one port to all ports. Switches will learn automatically what IP addresses are connected to each port and will only direct messages to the correct port. This limits the domain of collision and separates Ethernet segments. While hubs are slightly less expensive it is better to use switches whenever possible. Install only industrial Ethernet network components in an industrial environment. Hirschman is a common supplier of industrial Ethernet switches and hubs. Framing: There are two types of framing used on Ethernet networks: Ethernet II and In simplest terms, these are used within the TCP header and footer of the message. While some Ethernet devices (such as PCs) can handle either type of framing, some (such as certain PLCs) may need to be programmed for the specific type of framing in use. All industrial devices on an Ethernet network need to use the same framing in order to successfully communicate. The SMVector drive's MB TCP/IP adapter supports framing only. The 940 PositionServo drive's MB TCP/IP adapter supports only framing also. MB TCP/IP port number: Developers may ask which port number to direct MB TCP/IP communications to. Use port 502. This is specified in the MB TCP/IP protocol and does not need to be configured in the drive nor any other MB TCP/IP compatible device. It should be noted that some Ethernet switches may block access to port 502 as it is not a commonly accessed port outside of automation applications. If you can ping a node but it will not respond to MB TCP/IP messages then the switch MAY be a problem. MAC address: The MAC address of an Ethernet node is its permanent hardware address. Consider it like a serial number for the unit. Some Ethernet devices (such as some PLCs) require a utility (called a Boot P server) to assign their IP address. This is not necessary for any current AC Tech product. 2 AN 0024/A1 June 2007

3 IP addressing: An IP address is the logical address of the Ethernet node. Every device on an Ethernet network requires a unique IP address. An IP address is made up of 4 numbers (each with a value of 1-255) called octets separated by periods (i.e ). They are called Octets as they are made up of eight bits. The IP address of the SMVector drive and 940 PositionServo are set by the programming buttons locally on the drive itself. In order for successful communications, all IP addresses must be on the same local subnet. This is accomplished by subnet masking. Subnet masking: Subnet masking is used to define subnets. For our purposes, subnets are basically lists of addresses allowed to communicate to each other. This is done by a Boolean <and> comparison of the IP addresses. The subnet mask creates the Boolean <and> pattern to determine which bits need to match between the two IP addresses. This is more easily understood using binary numbers. In the following examples note that the subnet mask shows that for two addresses to be on the same subnet, every bit location denoted by a 1 in the subnet must match between the two IP addresses: Example #1 IP address: Binary Equivalent of IP address : Subnet Mask: Binary Equivalent of subnet mask: IP address #1: Binary Equivalent of IP address # Since all bits denoted by the subnet mask do match, both IP addresses are on the same subnet and communication is allowed. Example#2 IP address: Binary Equivalent of IP address : Subnet Mask: Binary Equivalent of subnet mask: IP address #2: Binary Equivalent of IP address # Since not all bits denoted by the subnet mask match, both IP addresses are NOT on the same subnet and communication is not allowed. 3 AN 0024/A1 June 2007

4 Default Gateway: A default gateway is a node on the network that serves as an access point to another network. A router is a gateway. To configure the IP address, subnet mask and default gateway of a PC: First, click on the start button to open the pop-up start menu. Then click on Control Panel Double click on Network Connections : Figure 3: Select [Control Panel] Figure 4: Select [Network Connections] 4 AN 0024/A1 June 2007

5 Double click on Local Area Connection : Figure 5: Select [Local Area Connection] Click once on Internet Protocol (TCP/IP) to select it then click on the Properties button: Figure 6: Select [Internet TCP/IP] This will allow you to access the TCPIP configuration for the PC as illustrated in Figure 7. Figure 7: Internet Protocol TCP/IP Properties 5 AN 0024/A1 June 2007

6 MB TCP/IP Map index number : One field in standard programming for MB TCP/IP communications (reads and writes) is the Map index number. This is used for various purposes in different target equipment. Bridges can use this as a table entry to define a particular routing, or address number on the other side of the bridge. Some devices use this as a data channel. The SMVector does not use the map index number so it can be left set to 0 for the master. The 940 PositionServo does not use the map index number either so it can also be left set to 0 for the master. Modbus register numbering: All AC Tech drives only use Modbus 4X register addresses for communications. Modbus register numbering is one greater than the drive s RAM register address (i.e. drive ram register 24 it's modbus register is 40025). It should be noted that the user must program the master to read and write the required number of registers for any given command. A series of successive writes is required to start the SMVector drive or change the speed. Refer to the product s Modbus manual for the progression of writes/reads required for your given application. Pinging: One useful utility to see if a node is on a network is to ping the node. From the command line simply type: Ping XXX.XXX.XXX.XXX (Put the desired IP address in place of XXX.XXX.XXX.XXX) If the node is reachable you will get reply s to the ping, if not you will see timeout messages. Remember to have the IP address of the PC set to the same subnet as the desired equipment. To get to the command line first click the start button, then click Run Enter cmd into the field and click the OK button. Figure 8: Run Figure 9: Command Link lights: Most Ethernet equipped automation devices and virtually all switches and hubs have link lights on them to show which ports have a connection. If a node is not reachable, check the link light first. If it is not illuminated and both devices are powered you may have a cabling problem. 6 AN 0024/A1 June 2007

7 Basic Ethernet cabling tips: Use a cable tester to check each cable prior to commissioning the network. Do not untwist the pairs more than ½ in length to the plug. Do not take off more than 1 of the jacket from the plug. Use gradual cable bends, do not crimp or kink the cable Do not splice Ethernet cabling. Keep the cabling separated from power cabling. Run it in its own conduit. If you need to cross power cabling do so at a right angle to minimize inductance. Is Ethernet IP the same as MB TCP/IP? No. While both run under TCP/IP for a transport layer, the data formatting is incompatible. They are different COM protocols. Note: For the drive to take start/stop commands from the Modbus master, set the drive s control source to NETWORK CONTROL. To allow the drive to take speed reference commands from the Modbus master, set the drive s speed reference to NETWORK REFERENCE. WARNING! Never reset a faulted drive locally! Always reset via the Modbus master. Failure to do so may result in unexpected operation. WARNING! Always send a low rotation speed command to a drive prior to changing direction. If both the direction and the speed setpoint are programmed to change at the same time, the drive may for a short time change direction and run at the wrong speed. 7 AN 0024/A1 June 2007