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Old March 29th, 2007, 10:32 AM   #1

PLC_talk is offline
Join Date: Oct 2006
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How to compute S7 Memory availibiity vis-a-vis CPU model no.

I am trying to corelate the S7 CPU specification data to the actual memory I get to use & somehow I am not able to come to a correct answer.
I have a CPU - 6ES7 414-4HJ04-0AB0, the manual specifies that this CPU has 700 KB of code & 700KB of data memory.
Q1. Is the data memory my S7 Byte/Word.DWord memory?
Q2. The Step7 allows me to write to max M65535 address only, and not max M700,000
Q3. Is there any relation between data memory & the Data area for Mxxxx?

Any wise advice?

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Old March 29th, 2007, 11:16 AM   #2
Ken M

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Data memory is the memory available to accommodate DBs. There are no DBs in a CPU when you get it, just empty space. You create them up to the limits of -
- maximum individual block size
- maximum number of individual blocks
- total available data memory.

The Mxxx.x memory in a CPU is already defined when it comes out of the box. Each model has a fixed address range regardless of the quantity of data memory. It can not be expanded or reduced. There is no relationship between the two. If you really need more than the number of M bits, bytes, words or double-words in the CPU you have to use one or more DBs to hold additional bits, bytes, etc

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Old March 30th, 2007, 07:30 AM   #3

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Thanks Ken
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