Siemens PLC Memory Structure

tahir4awan

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T
Join Date
Jun 2011
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Karachi
Posts
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As I always say I have been using Allen Bradley PLC. Now I have tried to learn about Siemens PLC.What I am able to understand is Siemens PLC memory is divided into three parts i.e Marker Memory, Local Memory and Data Block Memory. The function of Marker Memory is somewhat clear that it is a general purpose memory but what are local and data block memories? can anyone explain about these three types of memories?
 
In one book it is written there are three
parts of memory i.e Marker Memory (M), Local Memory (L) and Data Block Memory(DB) and in other book it is written there are three
parts of memory i.e Bit Memory (M), Variable Memory (V) and Special
Memory (SM)
 
tahir4awan said:
In one book it is written there are three
parts of memory i.e Marker Memory (M), Local Memory (L) and Data Block Memory(DB) and in other book it is written there are three
parts of memory i.e Bit Memory (M), Variable Memory (V) and Special
Memory (SM)
Click to expand...

Two different S7 PLC's
First for S7 300/400 using Step7 SImatic Manager (also TIA)
Second for S7 200 Using Microwin
 
The S7-300 and 400 series are equal concerning the memory area treatment (the size differs, of course).

The S5 and S7-200 is different. Those are also phased out, and should not be considered.

My recommendation would be to concentrate on the S7-300. If you are in the process/chemical industry, take the 400 and also with PCS7.

Kalle
 
The S7 300 and 400s have 3 Memory areas, load Memory, work memory and system memory. When you download the program to the PLC it gets downloaded to the load Memory. This is equivalent to a PC harddrive as is generally in the form of a memory card.

When the PLC is set to run, relevant parts of the program are transferred to work Memory and run from there. This is like RAM in a PC.

System memory is where the process image input/output tables, Memory bits, local stack, diagnostics and s7 counters and timers are stored.
 
Jieve said:
The S7 300 and 400s have 3 Memory areas, load Memory, work memory and system memory. When you download the program to the PLC it gets downloaded to the load Memory. This is equivalent to a PC harddrive as is generally in the form of a memory card.

When the PLC is set to run, relevant parts of the program are transferred to work Memory and run from there. This is like RAM in a PC.

System memory is where the process image input/output tables, Memory bits, local stack, diagnostics and s7 counters and timers are stored.
Click to expand...

All very nice but I think its clear from the the OP that he's questioning the program memory such as Data Blocks.

He's also confused about the different PLC's, the Siemens developed S7-300's and 400's and the Texas Instruments developed S7-200.

To the OP.

What specific PLC's are you working on?
 

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