Scalable CC-Link Repeater Hub FS-CCL-RPT
1. Basic features of CC-Link network
The physical layer of the fieldbus CC-Link and MODBUS is based on the RS485 interface technology, which is currently widely used. The CC-Link standard requires the RS485 network to maintain high reliability and stability at data rates up to 10 Mbps. Therefore, in the CC-Link standard, the RS485 technology has been further strictly defined and supplemented, including the network topology, segment, terminal, relay, branch and other concepts, and the cables, connectors, and medium used. Detailed technical specifications are also made for network components such as relays and hubs. 1.1. When the CC-Link standard specifies RS485 signal transmission, the bus-type network topology is adopted, and network components and concepts such as network segments, terminals, branches, repeaters, and connectors are proposed, as shown in Figure 1-1. When the cable length exceeds the distance specified by the CC-Link standard or the number of stations in the network exceeds the specified number, the repeater is used to divide the bus into two network segments, segment 1 and segment 2, and the head and tail of each network segment are called For the terminal.
1.2. Two terminal stations of a CC-Link RS485 network segment must be equipped with terminating resistors to suppress signal reflection. According to the characteristic impedance of the cable, the resistance of the terminating resistor is usually 110 ohms to 130 ohms, while other components in the network segment Stations cannot have terminating resistors, so it is important to determine which station is the terminal of the segment. 1.3. The CC-Link standard stipulates that the total number of site devices can be 64. When the number of sites in a segment is large, network communication may be abnormal and reliability may be reduced. In this case, devices such as repeaters or hubs must be used to divide into several segments. 1.4. The distance from a certain station to the RS485 trunk is called the branch line. The signal will generate echoes in the straight line to make the waveform distorted. Usually, the length of the branch line should not exceed 1 meter. It is the most ideal connection to eliminate the branch line by connecting the trunk to the terminal.
1.5. The CC-Link communication medium must use a dedicated cable conforming to the CC-Link standard. The maximum length of the communication cable in a CC-Link network segment is closely related to the baud rate. The maximum transmission rate that can be achieved by the entire CC-Link network depends on the maximum transmission rate. The network segment with the largest cable length. The general characteristics of the CC-Link cable and the maximum transmission distance at different baud rates are shown in Table 1-1 below:
2. The main purpose and characteristics of the four-star electronic CC-Link repeater hub
The four-star electronic CC-Link repeater hub has the following main uses: 2-1 Bus branch function (hub function): CC-Link RS485 is a network bus type topology, which does not allow branching, which increases wiring difficulties. Combining multiple FS-CCL-RPTs into a hub can change the CC-Link network bus topology to achieve a star-and-hybrid network structure for easy wiring. 2-2 Repeater function: The two interfaces of the CC-Link repeater can independently drive one CC-Link network segment, that is, the maximum transmission distance at the corresponding transmission rate can be extended. It is also possible to implement cascading. Thus, through the hybrid CC-Link network structure composed of repeaters, the transmission distance can reach several kilometers depending on the number of cascades (related to the transmission baud rate used). 2-3 Function of the isolator: Each interface of the CC-Link repeater or hub can be expanded into a “network segment” (which can be called “segment interface”), and each interface segment is electrically isolated, that is, segment It is electrically isolated from the segment. This is essential for protecting the interface, suppressing interference, and improving the stability of the network system. 2-4 Monitoring Diagnostic Function: The LED indicator on the CC-Link repeater can monitor the working status of each segment in the CC-Link network to provide reference for network diagnosis and troubleshooting. The four-star electronic CC-Link repeater has the following main features: The FS-CCL-RPT is used as a repeater in a single operation, and the N combinations can be expanded into 2N port hubs. For example, 2 can form a 4-port hub, and 3 can form a 6-port hub..., which is very flexible and convenient to use. Physical layer transparent transmission: The four-star electronic CC-Link repeater is transparently transmitted by the physical layer bit, and has nothing to do with the upper layer protocol. Therefore, it is applicable to all upper layer protocols based on RS485, such as MODBUS and other RS485. No distinction between master/slave interface, no input/output interface, no terminal/non-terminal node: For each RS485 interface, the master/slave can be connected to any interface. Baud rate 0~10Mbps adaptive: no switch settings or any software configuration required. Segment isolation: Each interface segment is isolated from each other. Cascading: Any interface segment can be cascaded through a CC-Link repeater to expand the number of interface segments.
3. Product characteristics and main technical parameters
4, external structure and terminal signal definition
5, internal block diagram
6. Application topology of four-star electronic CC-Link repeater hub
The four-star electronic FS-CCL-RPT repeater hub is very flexible and can be used as a repeater. Multiple can be combined into a hub. For example, N FS-CCL-RPT can be expanded to form a 2N port hub. Network, star network, tree network, and hybrid network topology. The user must correctly set the terminating resistor as shown in the figure, otherwise communication will not be possible. The ON and OFF in the figure indicate that the terminating resistor setting switch on the FS-CCL-RPT is turned to the corresponding position. The small red square indicates that the user needs to install the 120 ohm terminating resistor at this position. According to the RS485 specification, each station must be directly connected to the CC-Link bus, and no branch line should be generated. Otherwise, the signal will generate echoes in the branch line to cause signal distortion. 6.1. Application topology as a repeater: The FS-CCL-RPT is a CC-Link RS485 repeater when used alone. It only needs to be correctly wired and properly set the terminating resistor. It can work normally when the power is turned on, no other settings are needed. The following are the various network topologies used as repeaters. When the bus length exceeds the specified length or number of stations at the corresponding baud rate, the bus is divided into bus segment 1 and bus segment 2 by a repeater, each segment supporting a specified length and number of stations. The repeater in the figure below is the terminal in bus segment 1, the terminal in bus segment 2, and the terminal in bus segment 3.
Bus segment 1 is branched with a repeater and connected to another bus segment 2. The RS485 bus specification is the principle of taking a bus to the end, and a repeater must be installed at the branch point. The repeater in the figure below is a node in bus segment 1 and a terminal in bus segment 2.
Bus segment 1 and bus segment 2 are bridged with a repeater. The two-segment bus can be connected at any position with a repeater. The repeater in the following figure is a node in both bus segment 1 and bus segment 2.
6.2. Application topology as a hub: When using the FS-CCL-RPT to form a hub, you need to open the case and pull out the extension cable from the inside, and then connect the extension cable to the expansion socket of the previous module. N FS-CCL-RPT can be used to expand 2N port hubs, such as 2 can form 4 ports, 3 can form 6 ports, 4 can form 8 ports..., can use up to 10 FS-CCL -RPT expands into a 20-port hub. If you need to increase the number of interfaces, you can use cascading.
When using multiple FS-CCL-RPTs to form a hub, only one power supply is required. It is also possible to supply two or more power supply. At this time, it is a redundant power supply mode. When any one power supply loses power, it will automatically switch to another power supply, and the switching time is zero.
The four-star electronics FS-CCL-RPT is very flexible when used as a hub, enabling bus-type networks, star networks, tree networks, and hybrid network topologies. Below are various application topologies.
7.1 Why do terminal resistors must be installed at both ends (terminals) of an RS485 network segment? When the RS485 signal is transmitted in the cable, it will generate signal reflection, that is, the transmitting end will receive the reflected signal generated by itself, which is an error signal. This signal reflection can be eliminated when the resistance of the parallel connection resistor at the end of the cable is equal to the characteristic impedance of the cable. Generally, the characteristic impedance of the RS485 cable is 120 ohms, so the termination resistance installed at both ends of the cable is 120 ohms. 7.2. What are the communication protocols for the four-star electronic FS-CCL-RPT repeater hub? Can be used for CC-Link, MODBUS and normal RS485 free communication protocols. 7.3. How many FS-CCL-RPTs can I use to expand into a hub? The data given in our manual can be extended to 20 ports using 10 FS-CCL-RPTs. This is a conservative data. In fact, we tested the use of 25 units to expand, the work is very stable and reliable, but consider It is recommended that the user expands up to 10 units to the power supply and other factors. When there are more than 10 units, the cascade is used to expand. 7.4. How to determine the maximum communication rate that the entire network can reach? The FS-CCL-RPT repeater hub can be used to form a complex hybrid network. The length of each network segment varies. The maximum communication rate that can be achieved by the entire network depends on the longest network segment. If you want to increase the communication rate, you can use it. The relay or hub divides the longer segment to match your rate requirement. 7.5 What is the result of losing the terminating resistor in the network? When the cable is long or the communication speed is high, if a network segment loses the terminating resistor, it will definitely make the network unable to communicate normally, or it can only communicate at a very low rate. Regardless of the length of your network segment cable, you must properly install the terminating resistor. Everything is done according to the specifications to avoid communication failures, especially some annoying software failures. 7.6 What happens when the branch line in the RS485 network is too long? This will slow down the communication rate, and may also result in unreliable communication, or some site access and other uncertain soft faults. The length of the branch line is usually controlled within 1 meter. It is ideal to connect the bus to the terminal. The length of the branch line is zero, but it may be troublesome to connect the bus on one terminal. The RS485 interface of Siemens products, such as PROFIBUS, PPI and MPI, uses two pairs of terminals, which eliminates the problem of branch lines. 7.7. How to realize high-speed long-distance communication of CC-Link? When CC-Link communicates at high speed, such as communication speed of 5Mbps or more, the maximum cable cable can only reach 100 meters. Adding multiple repeaters or hubs will increase signal delay, increase cost, and troublesome power supply. Optical fiber transmission is currently the best cost-effective solution. Such as four-star electronic CC-Link fiber link adapters FO2-CCL-S and FO2-CCL-M.