Troubleshooting Memory Full Issue on Siemens S7-400 PLC

15-02-2025
MarkNightingale
15 comments
664
49

Question:

Yesterday, I visited a client's location and made a minor adjustment by converting a placeholder bool output to a real output in the existing hardware configuration. However, when I attempted to download the modification, I encountered a memory full error. Despite attempting to compress the memory as I have successfully done previously, I was unable to load the block to the PLC. Are there any alternative solutions I can explore before recommending a CPU upgrade to the customer? Cheers, Mark.

Top Replies

If you encounter an issue with your PLC, try stopping it, removing the problematic block from the online folder, downloading and adding a new block, and then restarting in run mode. This simple troubleshooting process can help resolve any programming errors efficiently.

16-02-2025
L D[AR2P#0.0]

According to MarkNightingale, no tags or markers were added, just a switch to an output already in the hardware configuration. Therefore, the entire program block that was altered needs to be downloaded. If the block is large, it may not be feasible due to lack of available free memory, despite minimal code changes. One potential solution for limited PLC memory is to divide existing program blocks into smaller segments. In my opinion, upgrading to the S7-1500 would be advisable over purchasing a larger and pricier S7-400 CPU, which would only provide temporary relief.

17-02-2025
JesperMP

Thank you for the responses. I will consider implementing your suggestions when I am back on location. Unfortunately, upgrading to the S7-1500 is not feasible due to the cost involved. I have a question regarding the CPU and VAT tables. Does storing 50 VAT tables in the CPU take up a significant amount of memory? I am considering deleting some of the tables to free up space. Any advice on this matter would be appreciated. Cheers, Mark.

18-02-2025
MarkNightingale

MarkVAT tables are not downloaded to the CPU as they are offline project components.

18-02-2025
JRW

According to JRW, MarkVAT tables are not downloaded to the CPU as they solely exist as offline project objects. However, if they are uploaded to the web server, they can be downloaded along with the hardware configuration. This means that MarkVAT tables can be accessed online if they are made available on the server.

18-02-2025
RVaughan

Hey Mark, it sounds like a frustrating situation! Before considering a CPU upgrade, you might want to check if there are any unnecessary programs or data that can be cleared from the PLC’s memory. Additionally, reviewing the current configurations to see if there's any redundant logic can help free up some space. Sometimes old projects or unused data blocks can take up valuable memory as well. If those options don’t pan out, consider breaking down the changes into smaller increments, if feasible. Good luck!

07-03-2025
Lisa Adams

Hey Mark! It sounds like a real challenge. Before recommending a CPU upgrade, you might want to check for any unused or redundant blocks in the existing program that you can delete to free up space. Also, consider consolidating data structures or optimizing logic to reduce memory consumption. Some PLCs also have options for organizing and archiving older data, which could help clear some memory. Best of luck!

07-03-2025
Emma Wright

Hey Mark! It sounds frustrating to run into that memory issue, especially after making adjustments. Before going for a CPU upgrade, have you tried checking for any unused data blocks or programs that can be deleted? Sometimes legacy code can take up more space than we realize. Additionally, you could look into optimizing your existing code or breaking down your modifications into smaller, more manageable blocks to see if that helps. Good luck!

24-04-2025
Abigail Morris

More Replies →

When considering an upgrade from the S7-400 to the S7-1500, cost is a significant factor to keep in mind. Depending on your current setup and needs, the expense of purchasing a medium or higher-end S7-400 CPU may actually be comparable to or even greater than replacing the entire S7-400 rack with an equivalent S7-1500 rack. It's important to plan for the future as well - if your plant will be in operation for many years to come, upgrading to the S7-1500 sooner rather than later may be necessary.

19-02-2025
JesperMP

RVaughan noted that files need to be accessible on the web server for them to be downloaded along with the hardware configuration. This could possibly be related to the contents within the blocks folder, which is crucial system data such as sdb.

20-02-2025
JRW

I was talking about the content in the blocks folder. I don't think any of the VAT tables are stored on the web server. Another thing to consider is what happens if I delete block OB1 and try to re-download it? Will it prompt a memory full message preventing me from downloading OB1 again? Thank you, Mark.

20-02-2025
MarkNightingale

Are you following LD's suggestion to do it online? Explore the convenience of online storage folders.

20-02-2025
JRW

A few years back, I had the opportunity to work with a complete ET200S controller, including a 300 in a separate case. I recall that in order to download the controller, there needed to be double the amount of free memory as the block size. This meant that whenever modifications were made to the largest block, I had to first delete the block along with several smaller ones online. After downloading the large block again, I would then proceed to redownload the smaller blocks as well.

20-02-2025
RVaughan

I'm concerned about accidentally deleting OB1 online and being unable to download it again. However, it does seem logical. Cheers, Mark.

20-02-2025
MarkNightingale

MarkNightingale shared his experience of making a minor modification at a customer site, changing a dummy bool output to a functional one without adding any additional tags or markers. However, when attempting to download the change, he encountered a memory full error. Despite trying to compress the memory, it was not possible to load the block to the PLC. Before suggesting a CPU upgrade to the customer, Mark is seeking alternative solutions. He also expressed concerns about potentially deleting OB1 online and being unable to re-download it. It is important to determine if the dummy output is located in the temp area or the marker (M) area, and whether the CPU's RAM or ROM memory is full. If everything is programmed to OB1, it may require a different programming approach. Siemens PLCs require double the memory for online changes compared to the block being used for download. In addition to the CPU's memory capacity, it is crucial to check if the memory card is full. Deleting unused DB areas or FB and FC blocks from the online project may free up memory. One suggestion is to allocate the dummy output to the %M or DB-block side for easier access in another subprogram. Adding a new OB block like OB30 might also help in managing memory constraints to execute the necessary changes.

20-02-2025
Lare

Hello Lare, thank you for your reply. The dummy output is located in the temporary area and not all components are in OB1. The program is comprehensive in nature. I attempted to stop the PLC before downloading the updated OB1, but unfortunately, it was unsuccessful. Recompiling everything also did not resolve the issue. I will be back at the customer site next week and plan to delete OB1 online as LD suggested. Thank you and regards, Mark.

20-02-2025
MarkNightingale

MarkNightingale inquired about what would happen if he deleted block OB1 and tried to re-download it, only to find that the memory was full and wouldn't allow the download. According to him, this issue shouldn't occur if the offline OB1 is the same size as the deleted OB1. It is advisable to check the memory status offline to see the available space and compare it with the size of OB1, which is usually not very large as it mainly calls other blocks. In case memory is insufficient to load OB1 without deleting it in the online program first, removing any unused code or DBs is recommended. It is crucial to be able to change the PLC program online without stopping the CPU. Some older and lower-end S7-400 CPUs used to require a RAM card for online editing, with the option to later transfer the program to a flash card for permanent storage. In certain instances, the RAM card was fixed in place and the program was saved by backup batteries. To address the specific issue, it is important to identify the CPU type and the card type in the CPU's card slot.

20-02-2025
JesperMP

Mark Nightingale replied to Lare, expressing gratitude for the response regarding the dummy output being in the temp area rather than in OB1. The program is extensive and not everything is in OB1. Despite attempting to put the PLC in stop before downloading the modified OB1 and recompiling everything, the issue persisted. Next week, Mark plans to address the problem by deleting OB1 online as suggested by LD. It seems unusual that changes were previously made to the PLC. Troubleshooting steps include checking memory usage in the PLC diagnostic window and considering the possibility of flash memory limitations in older CPUs. It may also be worth exploring the option of making online edits to different blocks. If the issue is related to areas outside of the CPU model's support, a different error message should appear. In the past, there were occasional memory errors during downloads on older S7 models. In some cases, restarting the PLC resolved the issue. It's crucial to monitor memory usage to prevent recurring errors.

20-02-2025
Lare

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Frequently Asked Questions (FAQ)

FAQ: 1. What could be causing the memory full issue on the Siemens S7-400 PLC after making minor adjustments?

Answer: - The memory full issue could be due to the increased memory usage caused by converting a placeholder bool output to a real output in the hardware configuration.

FAQ: 2. How can I troubleshoot and resolve the memory full error on the Siemens S7-400 PLC?

Answer: - You can try compressing the memory or optimizing the program to reduce memory usage. It's also essential to check for any unnecessary data or code that can be removed to free up memory space.

FAQ: 3. What alternative solutions can be explored to resolve the memory full error before considering a CPU upgrade?

Answer: - Before recommending a CPU upgrade, you can try optimizing the existing program by removing any redundant or unused code, variables, or data blocks. Additionally, you can consider splitting the program into smaller sections to reduce memory usage.

FAQ: 4. Is there a specific procedure to follow when compressing the memory on the Siemens S7-400 PLC to avoid memory full errors?

Answer: - When compressing memory, ensure to follow the proper guidelines provided by Siemens for the S7-400 PLC. Make sure to back up the existing program before compressing memory, and carefully review the impact of compression on the program's functionality.

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