SIEMENS PLC CPU memory

stevenPLC

Member
Join Date
Sep 2004
Posts
27
Hi all...

I'm using the Siemens CPU315-2DP. I think the Working Memory is only 128kb. But I think my program is large, and when downloaded into the CPU for execution, it uses up almost 100% of the working memory (I check this at the diagnostic - Module information, it's 98%). When this occur,I have problem to download and overwrite any FB or DB from my offline to the online project.Instead i have to delete the FB in online project then only i can download the FB from offline to online.And I think this may create problem when my program is already being run at the site and i need to do modification on site.

1)Can we in anyway set and add the Working Memory space of the CPU?

2)I have a MMC for this CPU which is used as the load memory for the progam.Can I make use of it as the working memory?How?

3)If the working memory really used up to 100%, what will actually happen to the execution of the downloaded program?Anyone try this before?

4) What's best solution to this problem?

Hope someone out there can give some solutions or suggestion...Thank you...
 
Hello stevenplc;

Work memory is not expandable for the S7-300 CPUs, not even with a MMC card. If you exceed work memory allovcation in runtime, your CPU will fault and you will have to reset to restart.
If you really cannot compress it (online properties of the CPU), then you have to upgrade the CPU; try a CPU 316-2 or even a CPU 317-2. No other choice, I'm afraid.
Unless you can reprogram the logic structure of your program to reduce memory usage: using multi-instance DBs for FBs, using STL code whenever possible...
Hope this helps,
Daniel Chartier
 
dchartier said:
Hello stevenplc;

, using STL code whenever possible...

Why does using STL code reduces memory? I know that FBD from siemens uses NOP 0 commands. (Switch FBD to STL and there are some NOP 0). That is the only reason I can think for STL being less memory consuming. What are the other memory reducing properties of STL programming? (If there are any)
 
STL reduces memory used

STL is more efficient in its use of program space than
either FBD or LAD. If you convert a simple program from
FBD or LAD to STL not only do you find a lot of NOP 0's but
also a lot of A(........) structures that are not required.

I suggest picking something simple you do in FBD or LAD.
Convert it to STL and then test it. Now trim away all the
excess STL that the conversion has created and retest.
If you are not confident with STL simply experiment until you
get the same functionality.

You should find that the STL code only uses about 2/3 the
program space used by FBD or LAD.

I use s7canopener (find using google) to view some Siemens
library blocks I use and then re-program them retaining the
features I need but removing those I don't require. This
can save quite a bit of program space.

Another tip is to check your online blocks versus your Step7
blocks. You may find you have obsolete blocks in your PLC
taking up program space that you have long ago deleted from your
Step7 project.

Anyway with a bit of work you should be able to easily get your
program memory usage back to 85%.
Good luck with it.......John Gaunt
 
Siemens PLC CPU memory concept

Hi All...

I am still doubt sth abt Siemens PLC CPU Memory.

I am now using CPU317-2. I found that without plugging in any MMC into this CPU, I couldn't download any program blocks and use it. Looks like it only has and depends on MMC as the memory and doesn't have any built-in memory AT ALL!! Am I right??

Is it every Siemens CPU must be used with MMC?

By the way, when I checked online the Module Information on the memory, there's stated "Load memory RAM + EPROM" ..What does this RAM + EPROM means? My understanding for now is EPROM means memory from the MMC, RAM maybe somewhere else..But after this experience, looks like both memory come from MMC and it actually means 1 type of memory only? Is that right, and same for all CPU?

Thanks for all the advices annd opinion..
 
all those 315's should be equipped with 128 kb .... except the 315F (192KB)

1) unit is equipped with RAM from manufacturer,
it's faster and without power looses data
2) unit is not working without MMC card,
simply because architecture does not allow that,
it hold your code&data while unit is power-off

... just imagine it like PC ... you have DIMM or DDR modules that mean work memory and HDD which is like load memory ... your pc will not boot without HDD equipped with OS too ...
 
Yes, every S7-300's of the latest generation require an MMC card to operate. On the other hand there is no backup battery.

If you search for "Siemens MMC" you will find that the architecture has been discussed many times allready on this forum.
 
CF card for TP 270

Hello everybody!!!

I use a TP 270 connected to a Siemens CPU 315-2 DP.

My problem is that when I have a power failure on the panel, all the data in my alarmbuffer disappears.

I bought a CF card to keep on to the data even if I have power failure. I created archives, with a storage path to the CF card.

I tried to make it work, but the alarm buffer is still empty when the power is back in the panel....:(

Anybody out there who has done something similar and knows any tricks to make it work ????

best regards Orense 🤞🏻
 
Hi orense.

It would have been better to start a new thread.

To answer your question:
Did you setup the archiving to write to the flash card ?
In Protool under "System" ... "Messages" ... "Settings" ... "Archives"-button, you have to change "Archive Alarm Messages" from "<No Archive>" to the name of the archive you created.
The procedure is similar in Win CC Flexible.
 
Oh I see that the problem may be something else.

The ordinary alarm buffer only displays what is in the RAM memory.
You have to create a page with a Message View that uses the archived alarms as the source. In the "General" tab for the Properties of the Message View, change from "Messages" to "Message Archive".
 
CF card

Hello Jesper!

Yes, I know. I noticed afterwards that I did not make a new thread but I posted a reply instead....little bit silly

to the problem...

Yes, I have made archives...One for alarm messages, one for event messages and one for system messages.

I also made storage paths for the card...

Do you know if this automatically saves the buffers to the card, or do I have to make a button to archive and retrieve the messages. I tried to make some alarms with the card inserted in the panel, checked the buffer to see that they were there. They were. Then I removed power, put the alarm signals in my VAT table low. Replaced power, but then the buffer was empty ???

Any ideas??
 
HeHe

Ok I noticed your second reply when I sent my second one....

Thanks alot...I will try to change buffer :-D
 
You dont have to program anything else.
Archiving should start automatically if you have made the steps I wrote.

But if you want to be able to remove the CF card, maybe for reading the content in a card reader, then you should program a pair of buttons to start and stop the archiving. This to avoid annoying error messages when you remove the card.
 
Messages

Thanks!

One more question... They way I have displayed alarm buffer before, is that I have a button which has a function which is on_click. When the function is activated it runs show_alarm_message_buffer...The buffer then appears in it,s own window...

Should I instead of doing it this way, do it like you say, make an own screen for alarms....and that screen reads from the archives ???

Is that the idea ???

Thanks alot Jesper :-D
 

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