2 - Schneider Electric CZ, s.r.o.

Memory structure
Controllers
Modicon M238 logic controller
Compact base for solutions with AFB
Memory structure
Internal RAM
User zone
%MW located variables
System + system variables +
relocation table
Symbols
(55 KB + 0.13 KB/symbols)
Program
(eg..41 bytes per ST instruction)
Unlocated variables
Libraries
CANopen variables
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Modicon M238 controllers offer great flexibility in
memory management. Depending on the model used,
they have a user memory zone of 1024 KB with
TM238 LFDC24DTS0 or TM238 LFAC24DRS0
bases.
This user memory zone is divided according to the
application program requirements and the volume
needed by the symbols, unlocated variables and
libraries required by the application.
The memory structure of Modicon M238 controllers is
shown opposite.
The table below lists the maximum memory capacities
depending on the model (values are given for
information only).
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3
Protected internal
RAM and first 1000
%MW words
10 KB
“Retain” and “Retain .
Persistent” remanent variables
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TM238 LFDC24DTS0, TM238 LFAC24DRS0
Internal RAM KB 2048
1 Located variables KB 120 (60,000 %MW)
2 System + system variables + relocation table KB 900
User zone KB 1000
3 Symbols KB 200 (max. 1000 symbols)
4 Program (including online program modification) As required by the application, within the limits of the size
5 Unlocated variables
6 Libraries
7 CANopen variables KB
of the user zone
115 + 10 per slave
Protected internal RAM KB 10
8 “Retain” variables Bytes 8168
8 “Retain Persistent” variables Bytes 400
8 First 1000 %MW words Bytes 2000
Storing variables
Remanent variables can be one of two types depending on their declaration in the application:
v v “Retain” variables, 8168 bytes maximum
v v “Retain Persistent” variables, 400 bytes maximum.
The first 1000 located variables 1 (first 1000 %MW words) and all the unlocated variables 5 configured as “Retain”
and “Retain Persistent” type are backed up by the internal battery or by the optional external battery. They are
maintained when the power returns if the startup context allows this (see “Restart context” below).
In addition, “Retain Persistent” type variables are maintained on a change of application if the startup context
allows this (see “Restart context” below).
Restart context
The state of the remanent memory before disconnection is restored on the next power-up when the internal
battery and/or the optional external battery is/are capable of protecting the internal RAM (no memory checksum
error).
If the internal battery or optional external battery does not have enough charge to back up the internal RAM, the
values of the “Retain” and “Retain Persistent” remanent variables are reset to 0.
In SoMachine V3, a new option accessible by configuration allows the choice of 3 modes to restart after powering
off the controller; run / stop / original state when powered off. In this third case, the optional battery is required in
case of powering off more than three days (autonomy of the battery after an initial charge of 22 hours ). If there is
no optional battery, the controller will start in the stop mode after a three-day power off.
The external battery can be monitored by the GetBatteryLevel software function, and its charging status is visible
from the status of the Batt LED on the front of the controller.
Storing the program
Regardless of the context and status of the internal battery and/or optional external battery, the program is backed
up in the Flash RAM during the “boot application” creation procedure (SoMachine software procedure).
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