Siemens SIMATIC S7-300 Series Reference Manual page 185

System memory
System memory is an integrated CPU RAM memory. This system memory
contains the operand areas (e.g. timers, counters, memory bits) and data areas
³ required internally by the operating system (e.g. communication buffer).
System state list
The system status list contains data describing the current status of an S7-300.
You can use it to gain an overview of the following at any time:
S S7-300 configuration
S Current CPU configuration and the configurable signal modules
S The current states and sequences in the CPU and the configurable signal
modules.
STEP 7
Programming language for developing user programs for SIMATIC S7 PLCs.
Substitute value
Substitute values are configurable values which output modules transmit to the
process when the CPU switches to STOP mode.
In the event of an input access error, a substitute value can be written to the
accumulator instead of the input value which could not be read (SFC 44).
Terminating resistor
A resistance for terminating a data transmission line. Avoids reflections.
Times
Times are integrated in ³ CPU system memory. The contents of the "timer cells"
are updated automatically by the operating system, asynchronously to the user
program. STEP 7 instructions are used to define the exact function of the timer
cells (for example on-delay) and initiate their execution (e.g. start).
Timer
³ Times
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01
Glossary
Glossary-15