Memory Mapping
RAM Memory Organization
Introduction
This section describes the RAM (Random Access Memory) size for different areas of the Modicon
M258 Logic Controller.
Memory Mapping
The RAM size is 64 Mbytes.
The RAM is composed of 2 areas:
dedicated application memory
OS memory
This table describes the dedicated application memory:
Area
System area
128 Kbytes
User area
10 Mbytes
Element
System Area Mappable Addresses
%MW0...%MW59999
System and diagnostic variables
(%MW60000...%MW60199)
( see page 27 )
This memory is accessible through Modbus requests only.
These must be read-only requests.
Dynamic Memory Area: Read Relocation Table
(%MW60200...%MW61999)
( see page 32 )
This memory is accessible through Modbus requests only.
These can be read or write requests. However, if this memory is declared in the relocation table, these must be read-only requests.
System and diagnostic variables
(%MW62000...%MW62199)
( see page 27 )
This memory is accessible through Modbus requests only.
These can be read or write requests.
Dynamic Memory Area: Write Relocation Table
(%MW62200...%MW63999)
( see page 32 )
This memory is accessible through Modbus requests only.
These can be read or write requests. However, if this memory is declared in the relocation table, it must write-only requests.
Reserved
Retains Data ( see page 28 )
Persistent Data
( see page 28 )
Symbols
Variables
Application
Libraries
Size
125000 bytes
3000 bytes
32 ko
64 ko
Dynamic allocation
26
EIO0000004135 09/2020
Memory Mapping
System and Diagnostic Variables
Variables
PLC_R
PLC_W
ETH_R
ETH_W
SERIAL_R
SERIAL_W
TM5_MODULE_R
PROFIBUS_R
Description
Structure of controller read only system variables.
Structure of controller read/write system variables.
Structure of Ethernet read only system variables.
Structure of Ethernet read/write system variables.
Structure of Serial Lines read only system variables.
Structure of Serial Lines read / write system variables.
Structure of TM5 modules read only system variables.
Structure of Profibus read system variables.
For more information on System and Diagnostic Variables, refer to M258 PLCSystem Library
Guide .
Memory Addressing
This table describes the memory addressing for the address sizes Double Word (%MD), Word
(%MW), Byte (%MB), and Bit (%MX):
Double Words
%MD0
%MD1
%MD2
Words
%MW0
%MW1
%MW2
%MW3
%MW4
...
Bytes
%MB0
%MB1
%MB2
%MB3
%MB4
%MB5
%MB6
%MB7
...
...
%MB8
...
Bits
%MX0.7
%MX1.7
%MX2.7
%MX3.7
%MX4.7
%MX5.7
%MX6.7
%MX7.7
...
...
%MX8.7
...
...
...
...
...
...
...
...
...
...
...
...
...
%MX0.0
%MX1.0
%MX2.0
%MX3.0
%MX4.0
%MX5.0
%MX6.0
%MX7.0
...
...
%MX8.0
...
Example of overlap of memory ranges:
%MD0 contains %MB0 (...) %MB3, %MW0 contains %MB0 and %MB, %MW1 contains %MB2 and
%MB3.
NOTE: The Modbus communication is asynchronous with the application.
EIO0000004135 09/2020
27
