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Homer_BL

S7-1200 <-> S7-1200 Modbus via RS232

15 posts in this topic

Hi all! If I want to connect two S7-1200 CPUs with RS232 ports on both CPUs, and implement a Modbus RTU communication, what is the cable pinout of a connecting cable? Thanks.

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Whats your thought on RS232 vs the built-in ethernet ports for communication? Are you passing this over radio or something? Edited by jrw

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Then why use RS232, just use the built in ethernet with Tsend and Trcv Done Why waste money/time on the RS232 modules? Edited by jrw

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What is this? Gestapo questioning? I just want to know cable pinout....

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Yes- it is If you dont know RS232 pin-outs (this is a world standard) then you need to find another profession . Thats a fancy word for job

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Homer, jrw was just trying to be helpful and suggest an alternative. No reason to get defensive. Your either jrw. That said (moderator hat off now), I agree, Ethernet would be a far better approach than making a custom serial cable and having to configure Modbus communications. If you want the connection pinout for the port, it should be documented in the S7-1200 manuals somewhere. Cross the send and receive wires, and you should be in business. Might also simply take a null modem cable.

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Hi, Cross! As you can see, there are al least four ways to make a serial cable. I wanted someone with expirience help me selec cable to spare my soldering efforts. No problem if you do can not help me, just be quiet. Regarding ethernet comm, it is clear, it is simple, but it is not challenge. :) I have here two S7-1200 with RS232, I have time to spend, so why not try Modbus? Someday maybe I'll need it, and then I will not have to spend pecious time to experiment with this. I repeat, if someone DOES NOT know answer to my question, NO PROBLEM, but do not try to write about something different. I am sick of 'geniuses'. :) Best regards. Untitled-1.pdf

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Better late then never. Here is pinout info for rs232 with CM-1241 Module. Manual p325 (rs485) p326 (rs232) and a link for rs485 My link Regards Tom 232.bmp

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Quite frankly after your negative attitude, I am shocked anyone actually helped you. I certainly would not have. Watch the tone of your posts in the future.

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Crossbow, noone helped me. I asked about cable, they tell me about port. And, what's wrong with my tone?

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So you got the port info and can't determine how to make a cable that connects to it? If you had said at the beginning you were just doing a test, then most people would not have tried to recommend better solutions. People were responding and trying to help you design a good system, and help you do it with a lesser amount of effort, and you reply with: Gestapo questioning? I am sick of "geniuses". Keep in mind these people do this for free, in their spare time, and nobody HAS to respond to you. Treat people with more respect and you might get more responses. And if you keep in mind that what you are trying to do is not something that would be ideal in a real world situation, then what makes you think someone here on the forums has done it before? People here were polite and responded to you with recommendations.

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Homer_BL: If you're new to Modbus, the pinout is just the beginning of opening a box with a whole lot of more questions. I guess you will be needing more help in the future, so I would not tell anyone to "be quiet" if they don't have the exact answer you are looking for. This is a PUBLIC forum where anyone is allowed to chime in a topic to share thoughts, ideas, and the reasons behind. All in a respective and polite manner. Even if a reply is not the one you are looking for, it might help you step away from your initial idea and give you a better one. If you need an exact answer and nothing else; call Siemens.

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No doubt, your tone is keeping your question from being answered now. I'm sure at least three of us now involved in this thread know your answer. JRW's initial question was a very good one. Simply answering his question instead of getting an attitude would have probably gotten you an answer 10 replies ago. Most of us help for the simple satisfaction of sharing knowledge, knowing that this knowledge pool will be here when we need it, and an occasional thanks. We're not required to give answers and are much less likely too when a poor attitude is involved.

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hi all. I need to use the MODBUS RTU. I can not use ethernet because the two PLCs have different IPs (design motifs). I am using the CM 1241 RS232 modules and do not know what type of null modem use. I tried with the basic configuration of 3-pin, 2,3 and 5 (2 and 3 crossed) but I have not been successful. Would have to use all pins except the 9? and few are crossed or bridged? you know the exact configuration? I have to say is the first time I taste a MODBUS RTU communication and I have no experience. Edit: I've solved the problem with this configuration. Now, I've another question. I want to send and receive another struct (sending struct and receiving struct are in the master and the slave and they are equal). Struct to send is "pedidos-trama" and the struct to receive is "portabobinas". What data would have to allocate data_add and data_len (MB_MASTER) with the example of the picture? thanks tintoretto Edited by tintoretto

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