Siemens SIMATIC S7-400 Hardware And Installation Manual page 286

Glossary
S
Scan Cycle Time The scan cycle time is the time the CPU takes to run the user program
once through.
Scan Rate The scan rate defines how often GD packets are sent and received on
the basis of the CPU cycle.
SFB
SFC
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 System diagnostics is the detection, evaluation, and reporting of errors
Diagnostics 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 A system function (SFC) is a function integrated in the CPU operating
(SFC) system which can be called in the user program when required.
Glossary-12
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System Function Block
System Function
S7-400 and M7-400 Programmable Controllers, Installation Manual
C79000-G7076-C424-01