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Posted to dev@plc4x.apache.org by "zhy1378 (via GitHub)" <gi...@apache.org> on 2024/01/09 17:50:14 UTC
[D] How do I configure the PLC memory address to start at 0 instead of 1 when using PLC4j Modbus-TCP?
GitHub user zhy1378 created a discussion: How do I configure the PLC memory address to start at 0 instead of 1 when using PLC4j Modbus-TCP?
I'm using PLC4j's Modbus-TCP implementation to communicate with a Siemens S7-200 PLC. The PLC addresses memory locations starting at 0, but PLC4j requires addresses to start at 1 when adding register items. This prevents me from reading address 0 in the PLC.
While other PLC brands may start addressing at 1, Siemens PLCs start at 0. So I believe the address checking in the addItem() method is not appropriate in this case.
Is there a way to configure PLC4j to allow starting register addresses at 0 instead of 1? Or alternatively, is there a way to disable the address validation check so I can specify address 0? I need to be able to read the full range of PLC memory including location 0.
GitHub link: https://github.com/apache/plc4x/discussions/1330
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Re: [D] How do I configure the PLC memory address to start at 0 instead of 1 when using PLC4j Modbus-TCP?
Posted by "zhy1378 (via GitHub)" <gi...@apache.org>.
GitHub user zhy1378 added a comment to the discussion: How do I configure the PLC memory address to start at 0 instead of 1 when using PLC4j Modbus-TCP?
Hi, thanks for your answer.
Your suggestion is what I am doing right now - using address 1 as the starting address instead of 0.
Arrays and lists begin at 0, not 1, in most programming languages. I have been programming for over 10 years before using PLCs and Modbus-TCP, and having addresses start at 0 aligns better with my experience.
Even though the Modbus specification defines 1 as the starting address, stopping the check for non-zero addresses would likely work better in this situation and provide more compatibility. Do you agree?
While the Modbus standard specifies starting at 1, allowing a starting address of 0 seems more intuitive for those with a programming background. Disabling the address validation would enable full compatibility with PLCs like Siemens that start addressing memory at 0. Given my background, starting addresses at 0 feels more natural as well. What are your thoughts on disabling the address check?
GitHub link: https://github.com/apache/plc4x/discussions/1330#discussioncomment-8074254
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Re: [D] How do I configure the PLC memory address to start at 0 instead of 1 when using PLC4j Modbus-TCP?
Posted by "chrisdutz (via GitHub)" <gi...@apache.org>.
GitHub user chrisdutz added a comment to the discussion: How do I configure the PLC memory address to start at 0 instead of 1 when using PLC4j Modbus-TCP?
I agree, c that this seems odd for us IT folks. However what do you think would happen, if we removed that check? We'd be sending -1 on the wire.
We could add a config option to the connection string to start at 0, but that's I guess the only way to solve this.
GitHub link: https://github.com/apache/plc4x/discussions/1330#discussioncomment-8075894
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Re: [D] How do I configure the PLC memory address to start at 0 instead of 1 when using PLC4j Modbus-TCP?
Posted by "chrisdutz (via GitHub)" <gi...@apache.org>.
GitHub user chrisdutz added a comment to the discussion: How do I configure the PLC memory address to start at 0 instead of 1 when using PLC4j Modbus-TCP?
Hi,
According to the Modbus spec there technically is no Register 0 or coil 0 ... however many vendors don't implement their protocol-stack correcly according to this spec.
If you read Coil 1, all addresses are sent over the wire as x-1 ... so 1 becomes 0 ... please try if simply adding 1 to all your addresses gives you the results you're looking for.
GitHub link: https://github.com/apache/plc4x/discussions/1330#discussioncomment-8070157
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