Siemens SIMATIC S7-300 Hardware And Installation Manual page 249

Clock memory bits
Memories that can be used for clocking purposes in the user program (1 memory
byte).
Note
Note in the case of S7-300 CPUs that the clock memory byte is not overwritten in
the user program.
Timer
--> Timer
Token
Access right on bus
Reduction factor
The reduction rate determines the send/receive frequency for --> GD packets on
the basis of the CPU cycle.
Time-of-day interrupt
--> Interrupt, Time-of-day
Varistor
Voltage-independent resistor
Delay Interrupt
--> Interrupt, Delay
Watchdog Interrupt
--> Interrupt, Watchdog
Counter
Counters are part of CPU --> system memory. The content of "Counter cells" can
be modified by STEP 7 instructions (e.g. up/down count).
S7-300 Programmable Controller Hardware and Installation
A5E00105492-02
Glossary
13-15