Functional diagram

The 40 and 50 series central units memory is composed of two distinct areas:

– A SRAM memory where the user program and data is loaded.

– A Flash EPROM memory which contains:

– a backup of the user program with the program constants,

– the configuration data,

– and the system program protected against access from the user program.

An incorporated battery, which is available only in the 50 series, also enables the backup of

internal variables.

The user program is a set of universal functions conceived by the constructor to cover all

applications and ensure all the basic PLC functions. It is developed with the AC31GRAF

software. After being translated into instructions understable by the central unit it is loaded in

RUN or STOP mode into the SRAM and then saved from the SRAM to the Flash EPROM.

Thereby, at each program launch the user program, saved in the Flash EPROM, is copied to

the SRAM for processing by the microprocessor (Figure 1-3).

The structure of the system program memory, the user program, the inputs / outputs and

internal variables are described in the annex (mapping).

Program execution

The central unit microprocessor ensures the cyclic execution of the system as shown in

Figure 1-4.

The internal processing:

– PLC monitoring and control

– and processing requests from the terminal operator,

is executed in parallel with the previously described cycle.

The main program is processed sequentially. It may call up to a maximum of 12 sub-programs.

Each sub-program may be called numerous times in the main program.