Siemens SIMATIC S7-300 Series Reference Manual page 183

RAM
A RAM (Random Access Memory, read/write) is a semiconductor chip.
Reduction factor
The reduction factor based on CPU cycle time determines the frequency ³ of
GD package exchange.
Reference ground
³ Ground
Reference potential
Potential with reference to which the voltages of participating circuits are
observed and/or measured.
Restart
When a central processing unit is started up (e.g. by switching the mode selector
from STOP to RUN or by switching the power on), organization block OB 100
(complete restart) is executed before cyclic program execution commences (OB
1). On restart the input process image is read and the STEP 7- user program is
executed, starting at the first OB1 instruction.
Retentivity
A memory area is retentive if its contents are retained even after a power failure
and transition from STOP to RUN. The volatile area of memory markers, timers
and counters is reset following a power failure and a transition from the STOP
mode to the RUN mode.
The following can be made retentive:
S Bit memories
S S7 timers (not for CPU 312 IFM)
S S7 counters
S Data areas (only with memory card or integral EPROM)
Runtime error
Errors occurring during program execution in the PLC (that is, not in the
process).
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01
Glossary
Glossary-13