bottleneck message when downloading to Siemens S7 318-2 processor

Hello,

Why is it that when making more than a few networks and adding a few new tags, I must always reset the plc memory before downloading the new blocks? I find this to be a huge problem compared to Allen Bradley because I never have to worry about the plc stopping or a block not functioning anymore because it will not download due to some bottleneck error. Is there something that I am missing? Normally with AB I make as many changes as I want and then just download and no questions pop up or I don't need to worry about the plc or machine stopping because of my new changes. I am bit a afraid with S7 to make changes while the machine is running because sometimes I get this bottleneck error and asks me if I want to compress the blocks to save memory. The plc still has over 50% memory left. How can I avoid this?

Thanks!

PK

When you download a block the old one doesn't get deleted, so after a while the memory gets full up. This is when you need to compress it all the old blocks the get deleted. If you are doing this all the time you may want to consider getting a bigger memory module.

If you want the Bottleneck Error message to go away, then you should get a larger MMC.

I raised a question about this error and was told that the message is normal when the offline program size becomes larger than the available free space on the MMC. For example, when I downloaded my entire project, the download bottleneck warning I received indicated that my program required 33014, but only 32532 of 65536 (64KB MMC) was available. About 50 percent as you observe with your project.

However, my project downloads just fine. My understanding is during downloads the blocks are loaded one at a time, but you need enough free space to create a copy of that block as Marshy stated. The only free space you need is enough for the largest offline block to create a copy, sort of a swap space. My largest block size was about 4K, so there was plenty of room in the remaining 32K of free space.

So chances are, if your largest block is smaller than your free memory space, you will just have to live with this annoying message. Otherwise, get a larger MMC.

As for A-B, RSLogix knows how much memory the SLC you are downloading to has - you defined it in your Controller Properties. So when you compile, you will be warned. The Simatic Manager on the other hand, does not know what size MMC you are using. So, it can not warn you before downloading.