20090402 Daily question: Today let’s discuss the communication connection resources of Siemens S7.

PG refers to the online Step7 connection. Whether it’s a laptop, a Siemens PG desktop computer, or your server, as long as there is one Step7 system monitoring the PLC, that PLC will have one PG connection occupied. OP refers to the touch screen. It specifically refers to Siemens touchscreens. For example, if you have an MP277 connected online to a CPU, then that CPU will have one OP connection occupied. It should be noted that when WinCC uses built-in drivers to connect to a PLC, it is often considered an OP connection. I still don’t fully understand S7 basic communication connections at the moment. Understand it simply like this for now. For example, when the CPUs of several PLCs are interconnected, data communication can be carried out using read/write commands via the MPI interface. Once reading and writing are complete, the communication resources are released. Simply put, for example, one 315‑2DP and one 314 communicate using read/write commands via MPI; if communication is in progress, it occupies one S7 basic communication connection resource, whereas once the communication is completed, no S7 basic communication connection is used. / An S7 connection refers to a connection that uses the S7 protocol. Many HMI software applications use the S7 protocol to connect to PLCs, which consumes S7 connections. SimaticNet also occupies the S7 connection most of the time. The third-party touchscreens in Quito also use S7 connections, and the third-party OPC Servers in Quito likewise use S7 connections. However, note that the connection type for Top OPC and Kep OPC can be changed. The maximum number of connections can be seen when the group has limited CPU communication resources. As for how to set it up, it needs to be determined based on the actual circumstances.

A small suggestion: Could these questions be asked in several rounds? So that everyone can answer and learn easily.

I remember that the CP5611 can be connected to a maximum of two host computers via the MPI interface, while with Profibus DP it can be connected to up to 5 host computers. I’m not sure if this is correct

The OP raised a good question; I had been wondering the same thing. Pay attention – there’s an exact answer! JieKong General Manager’s Blog: How many host computers can a Siemens S7-300/400 be connected to? "How many host computers can a Siemens S7-300/400 be connected to? This is a question that users often ask us, and I couldn’t give an accurate answer; I would have to respond vaguely, and after searching through various resources I still found no solution, which frustrated me for many years. Recently, our company had the opportunity to work on a large-scale project in which all of Siemens’ communication methods were utilized, with a large number of host computers involved. Through testing, we finally obtained an exact answer, fulfilling my long-held desire. I hope this will also be helpful to those who are interested. Siemens offers three main communication methods: MPI, PROFIBUS, and Ethernet. With the CP5611 card used in the host computer, up to 3 host computers can be connected; using the CP5613 card, up to 5 host computers can be connected. With PROFIBUS, using the CP5611 card allows up to 5 host computers to be connected, while the CP5613 card enables connection to up to 11 host computers. For Ethernet, using a regular network card allows up to 8 host computers to be connected, whereas the CP1613 card allows connection to up to 30 host computers. The above numbers are based on the number of connections allowed by the CPU.

What was said above isn’t entirely correct; in fact, the engineers in Siemens’ CS department who are responsible for Simatic Net support are also a bit confused themselves. Manager Gong’s statement isn’t entirely correct either. His test is based on the JieKong test. It was probably the Olympic Bird’s Nest project that provided him with a better testing environment. Otherwise, it is usually difficult to have a good testing environment. In the host computer, MPI uses the CP5611 card, and up to 3 host computers can be connected; for Siemens solutions, PLC+PC configurations cannot have more than 8 devices. Let’s assume there is only 1 PLC for now; then can it connect to 7 host computers? My tests showed that it doesn’t work: the S7-300 can connect to only 4 devices, while the S7-400 \"should\" be able to connect to 7. I have 6 devices on site, and they were all connected successfully. When using the CP5613 card in the host computer, up to 5 host computers can be connected; \"the number of computers that can be connected to each PLC has nothing to do with the CP5613.\" The difference between CP5613 and CP5611 lies in the number of PLCs that each computer can be connected to. Of course, the hardware implementation and software implementation of the Profibus protocol are also one of its differences. ” With the CP5611 card in the host computer, PROFIBUS can be used to connect up to 5 host computers; with the CP5613 card, up to 11 host computers can be connected. In principle, there is a difference in the way CP5611 uses the PROFIBUS protocol to connect to S7 devices – WinCC can use its built-in PROFIBUS driver to establish connections via CP5611, while Jekong can also use its built-in PROFIBUS driver for such connections. Other software, on the other hand, can only establish connections through SimaticNet. The computer appears as a Category 2 master station in the DP framework; only the CPU is a Category 1 master station. The number of type II master stations should definitely not exceed 2! ” A typical Dp bus should have one primary master station; Siemens also allows only one such primary master station, with as few secondary master stations as possible. Downward, there can be 1-n slaves. The situation with CP5613 is similar. When I use the CP5611, there are also only 2 computers. For more than 2 computers, it is highly not recommended to use a bus for connection. The system’s risk coefficient is too high. --Have you seen that engineering company under Siemens use the Cp5611 or Cp5613 to connect multiple computers to a PLC? You should know that adding a CP343-1 to a 300 CPU costs less than 8K, and it can be connected to 8 computers. If there are 8 computers at the higher level, then 8 CP5611 units are required, costing 8X3100 = 2400 yuan. The speed is extremely slow, and the risk level is high as well. CP5613 is even more expensive. For Ethernet, using a regular network card on the host computer allows connection to up to 8 host computers; using the CP1613 card enables connection to up to 30 host computers. The above numbers of host computers are attainable provided that the CPU’s connection capacity permits it. This is even more incorrect. Whether the host computer uses a regular Ethernet card or a CP1613, the difference lies in how many PLC stations a single computer can connect to, rather than how many computers a single PLC station can connect to. 300 CPU + CP343-1, as well as a 300 CPU with PN; up to 8 computers can be connected via Ethernet. 400 CPU + Cp443-1, as well as 400 CPUs with PN. A maximum of 31 (32 according to the manual) or 63 computers can be connected. The boundary is the CPU414-3; those above this value, including it itself, have a connection count of 64, while those below it have 32. But once again, we need to return to practical engineering applications. For more than 8 computer connections, it is recommended to use a C/S architecture; a single PLC should not be connected to so many computers, as the communication load would be too high. The true limitation, or at the very least the primary limitation, is the number of connection resources available on the CPU itself; followed by limitations related to its performance in actual operational conditions. This is actually more important. Many show a huge difference from the theoretical values.

Also, what is cited on the second floor is a post I made on Siemens’ official website forum. Not a single word was missed; the emotions were just copied with Ctrl-C + Ctrl-V. Tell me, how should I rate you?

Let me intercede on behalf of the 2nd floor. Don’t deduct points, as it wasn’t copied from this forum. And he thought your speech was good, which shows that you understood it well. No more than 5 points, okay? Of course, it’s up to you regarding your question; this is just a reference.

In the CPU communication resource settings of 300, what is the specific meaning of the configuration values related to PG, OP, basic S7 communication, S7 communication, and already configured settings? It is the minimum number of connections reserved for this connection resource. For example, in the case of a CPU of type 315-2PN, the maximum number of connected resources is 16. The reserved value for PG is set to 1; thus, no matter what the value of OP+s7 basic+s7 is, it cannot exceed 15, as at least one resource must be reserved for PG. This 1 represents the minimum number of connections reserved for Po; it does not mean that there can be only 1 PG connection. Similarly, the number of connection resources reserved for OP is 1, which means that at all times, at least one OP connection resource must be reserved for touchscreen devices. This linked resource cannot be occupied by any other communication; it must be reserved for the OP, with at least one reserved, although multiple can also be reserved. We can ignore S7 basic communication for now. Simply put, such resources are needed only when multiple PLCs communicate with each other using protocols like MPI. Of course, in reality it’s not that simple. S7 communication (configured) – this is not easy to understand. This refers to the total number when you configure the communication for the CPU in NetPro, with the connection type set to S7 connection. For example, in the 315-2PN model, if you insert 3 PC Stations, and within the OPC Server of those PC Stations you establish 1 connection of the S7 type to connect to this CPU. At the same time, you also enable this 315-2PN to communicate over Ethernet with another 414, using an S7 connection type as well. So for the S7 you see, the configured quantity should be 4. When 3 S7s are connected, it is from the CPU to the PC Station; when 1 S7 is connected, it is from the CPU to another CPU. Many, many people have misconceptions about these settings. This includes extensive technical support from Siemens’ CS department, as well as drivers provided by numerous manufacturers of configuration software. So, the best approach is to do it yourself, then observe the change in that quantity and think about it further. As a further clarification, although the number of connection resources for 315-2PN is 16, can you connect 16 computers, PLCs, or touchscreens through its built-in Ethernet interface? No, the number of connections through the Ethernet port of 315-2PN cannot exceed 8. The number of MPI connections as well cannot exceed 8. If you add another CP343-1, then the number of connections for that new CP343-1 also cannot exceed 8. In addition, the total number of connections across all interfaces – including the built-in Ethernet port, the CP343-1 ports, the MPI ports, and any other communication ports – must not exceed 16. This post was last edited by qiaopeng1231 on 2009-4-4 at 08:30

3. Why doesn’t the S7-400 have a value setting for this? Since the communication connection resources for 400 CPUs are allocated automatically and dynamically, with a minimum of 32 resources and 64 for higher-end models, Siemens no longer performs manual allocation by default. Allocated by the CPU itself. However, internally, one connection resource is reserved for each of PG and OP; these two resources must not be occupied by S7 or any other connections at any time. In other words, no matter how many computer stations or PLC stations you connect, when you want to perform online monitoring of programs (at which point they are considered PG stations), the CPU still retains at least 1 PG connection. When you want to add one more touchscreen, (at this point it is considered an OP station), the CPU still retains at least one OP connection.