Siemens SIMATIC S7-300 Manual page 119

Signal module
Signal modules (SMs) form the interface between the process and the automation system.
There are digital input and output modules (input/output module, digital) and analog input
and output modules (input/output module, analog).
Signal status list
The system status list contains data that describes the current status of an S7-300. You can
always use this list to obtain an overview of:
• The configuration of the S7-300
• The current CPU configuration and configurable signal modules
• The current states and processes in the CPU and in configurable signal modules.
Slave
A slave can only exchange data with a master after being requested to do so by the master.
STARTUP
The STARTUP mode is executed at the transition from STOP to RUN mode. It can be
triggered by means of the mode selector switch, or after power on, or by an operator action
on the programming device. An S7-300 performs a restart.
STEP 7
Programming software for the creation of user programs for SIMATIC S7 controllers.
Substitute value
Substitute values are parameterizable values which output modules transfer to the process
when the CPU switches to STOP mode.
In the event of an I/O access error, a substitute value can be written to the accumulator
instead of the input value which could not be read (SFC 44).
System diagnostics
System diagnostics is the detection, evaluation, and indication of faults/errors which occur
within the automation system. Examples of such error/faults are program errors or failures on
modules. System errors can be indicated by LEDs or in STEP 7.
System function
A system function (SFC) is a function integrated in the operating system of the CPU that can
be called when necessary in the STEP 7 user program.
System function block
A system function block (SFB) is a function block integrated in the operating system of the
CPU that can be called when necessary in the STEP 7 user program.
S7-300 CPU Data: CPU 315T-2 DP
Manual, 12/2005, A5E00427933-02
Glossary
Glossary-9