Operation Of The 40 And 50 Series Central Units; Functional Diagram - ABB AC 31 Technical Manual

3. Operation of the 40 and 50 series central units

3.1. Functional diagram

ABB Control - AC 31
1SBC 260400 R1001-b 06.99
Presentation / operation
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).
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