Siemens SIMATIC S7-400 Configuration And Use Manual page 21

Integrated Functions
The operating system of each CPU features the following integrated functions,
which simplify the user program considerably:
• Operating control and monitoring functions
• Functions for communication
• Functions for diagnostics
• Functions for transmission of data records
• Functions for program control
• Functions for interrupt handling
• Functions for generating messages
The integration of these functions in the operating system means that there is no
need for tedious programming and the cycle time load of the CPU is reduced.
Diagnostics Buffer
Each CPU features a diagnostics buffer, in which error and diagnostic messages
are entered and stored.
Messages are entered into the diagnostics buffer either by the CPU or other
modules. User-defined diagnostic messages can also be entered by the user
program.
These messages can be read by the programming device at any time. The date
and time of the entry is also included. Messages can also be sent to operator
control and monitoring stations. The diagnostics buffer entries cannot be
manipulated. The most recent 120 entries are retained even after "bootstrapping".
Automation System S7-400 Configuration and Use
A5E00442711-02
CPUs of the S7-400
2-5