Siemens S7-400 Installation Manual page 307

Signal Module
Signal modules (SMs) are the interface between the process and the
programmable controller. Signal modules comprise digital input and output
modules (I/O module, digital) and analog input and output modules (I/O module,
analog).
SRAM Backup
A static RAM: with the programmable modules of the M7-400 programmable
controller, part of the main memory is backed up as an SRAM.
STARTUP
The CPU goes through the STARTUP state during the transition from STOP to
RUN mode. It can be set using the mode selector on the CPU, following power-on,
or by an operation on the programming device.
STEP 7
Programming language for writing user programs for SIMATIC S7 programmable
controllers.
Substitute Value
Substitute values are values which are output to the process in the case of faulty
signal output modules or which are used in the user program instead of a process
variable in the case of faulty signal input modules. The substitute values can be
specified in advance by the user (for example, maintain old value).
System Diagnostics
System diagnostics is the detection, evaluation, and reporting of errors occurring
within the programmable controller. Examples of such errors are: program errors or
failures on modules. System errors can be indicated with LED indicators or by
STEP 7.
System Function (SFC)
A system function (SFC) is a function integrated in the CPU operating system
which can be called in the user program when required.
System Function Block (SFB)
A system function block (SFB) is a function block integrated in the CPU operating
system which can be called in the STEP 7 user program when required, just like a
function block (FB).
S7-400 and M7-400 Programmable Controllers Hardware and Installation
A5E00069481-04
Glossary
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