what percent Controllogix PLC memory can be used

Hi, I just want to know at what percents Controllogix PLC's Memory can be used.By now, My project use 40% memory. and the communication with ENET Ethernet card is slower than before.

What is the system overhead time slice set at?

What's mean system overhead time slice?

jkerekes said:

What is the system overhead time slice set at?

Click to expand...

Open your Controller Properties and check the Advanced Tab. You can check the "System Overhead Time Slice"(from now on i'll call it SOTS) here.

In essence, the SOTS is how much of the processor time you are dedicating to things that are not the main task. IE, Communications, Messaging, serial ascii stuff, etc.

If you run the Logix5000 Task Monitor against your device you can see how long the MainTask is taking to run and if it is overlapping w/ itself or anything like that. If you open the Processes tab here you can check how much CPU time your communications is taking for example.

My SOTS is set to 20%, does the communication include Controlnet and Ethernet/IP too, My SCADA system using Ethernet/IP(enet card) to communicate with the PLC, and I have three Racks of Controlnet I/O, if the I/O and Tags are increased, does it mean I need to increase SOTS too to maintain good communication pefermance? Thanks a lot!

Dravik said:

Open your Controller Properties and check the Advanced Tab. You can check the "System Overhead Time Slice"(from now on i'll call it SOTS) here.

In essence, the SOTS is how much of the processor time you are dedicating to things that are not the main task. IE, Communications, Messaging, serial ascii stuff, etc.

If you run the Logix5000 Task Monitor against your device you can see how long the MainTask is taking to run and if it is overlapping w/ itself or anything like that. If you open the Processes tab here you can check how much CPU time your communications is taking for example.

Click to expand...

What revision of processor are you running.

On V16 (i think) or later, you can use unused SOTS for regular processing, meaning you can set this high (i have tested this at 90%, with no detriment to the user code), but the system gets back to your code when system tasks are finished.

Your original question misled me, you asked about MEMORY, but SOTS is a CPU processing timing parameter, nothing to do with memory.

If you wanted to know about Memory.....

Free memory is used mainly for two things.

a. As a buffer area for online edits (remember the processor holds the "old" and "new" rungs, so you can switch between them in Test Edits, Ubtest Edits modes), and

b. To store a "list" of online edits that have been made. This is used when an offline project that is "out of date" tries to get online. The "list" is used, if it is big enough, to update an offline project, to allow it to go online. This is called "correlation".

All that said, there is no hard and fast rule for how much memory to leave free. Too little, online editing will be limited to a few rungs at a time, and "old" projects won't be allowed online (an upload will be necessary). There is no concept of "too much" free memory, the more the better, really, but it's got to be paid for.

So it boils down to an opinion, and mine is - I would be uncomforatble with less than 10% free memory.

If you have to buy your processor before the code is written, err on the side of caution, and buy a larger processor, then you won't be cutting the application or trying to swap it for a larger one.

If you can write the code first, there is a tool in the processor properties to estimate the memory size required for the program.

wilsonzhu said:

Hi, I just want to know at what percents Controllogix PLC's Memory can be used.By now, My project use 40% memory. and the communication with ENET Ethernet card is slower than before.

Click to expand...

What type of processor and version (SOTS really didn't function usefully until version 16)? What type of ethernet card? Are you really using an enet card, not an enbt card?

Anyway, 60 percent of your memory left seems like lots to me, without knowing the application of course. You do need memory to service communications, especially if you are running a lot of msg instructions (more than you can cache in the buffer alloted).

I would look closer at your ethernet card. Let's assume you have an enbt card. You can only use 5000 pps for throughput on an enbt. So, if you are using I/O over ethernet to say, point i/o, then the quantity and the RPI rate is important for this calculation. Also, tags on a Panel View Plus will have an effect on the pps for the enbt card, especially if you are running a high refresh rate on a screen with lots of tags.

You can use the built in web page on the enbt card for monitoring it. I would start there.

Also, search the knowledge base for more information on CIP connections or packets per second throughput. If you really have an enet card, look up the connection limit and pps for that card. I have never used one, but I don't believe its as capable as the enbt (not to mention then there is the en2t).

If you are post ver16, are you servicing comm or running the continuous task with left over cpu time?

See this thread for some more about time slice.
http://www.plctalk.net/qanda/showthread.php?t=51592