Glossary
Glossary-12
ET 200S Interface Module IM 151/CPU
A5E00058783-01
Timers (timer cells)
Timers are part of the system memory of the CPU. 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 (e.g. on-delay) and initiate their execution (e.g. start).
Token
Access right on bus
Transmission Rate
The transmission rate of a data transfer is measured in bits transmitted per
second (transmission rate = bit rate).
In the case of the ET 200S, transmission rates of 9.6 kbps to 12 Mbps are
possible.
User Memory
The user memory contains the code and data blocks of the user program. The
user memory can be integrated in the CPU (IM 151/CPU) or can be provided on
plug-in memory cards or memory modules. The user program is always
executed in the working memory of the CPU, however.
User Program
The SIMATIC system distinguishes between the operating system of the CPU
and user programs. The latter are created with the programming software
STEP 7
in the possible programming languages (ladder logic and statement list)
and saved in code blocks. Data is stored in data blocks.
Working Memory
The working memory is random-access memory in the CPU that is accessed
by the processor during program execution.
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