Siemens Simatic S7-300, Hardware And Installation Manual, Page: 235 / 242

Glossary
S7-300 Programmable Controller Hardware and Installation
A5E00105492-01
12-15
Timers
Timers are part of 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).
Token
Access right on bus
Transmission rate
Rate of data transfer (bps)
Ungrounded
Having no galvanic connection to ground
User memory
User memory contains --> code and --> data blocks of the user program. User
memory can be integrated in the CPU or stored on plug-in memory cards or
memory modules. However, user programs are always executed from --> CPU
working memory.
User program
The SIMATIC system distinguishes between the --> CPU operating system and
user programs. The latter are created with --> -->STEP 7 programming software in
optional programming languages (LAD and STL) and stored in code blocks. data is
stored in data blocks.
Varistor
Voltage-independent resistor
Watchdog Interrupt
--> Interrupt, Watchdog