Siemens SIMATIC S7-400 Installation Manual page 223

Timer (T)
Timers are an area in the system memory of the CPU. The contents of these timers
are updated by the operating system asynchronously to the user program. You can
use STEP 7 instructions to define the exact function of the timer (for example,
on-delay timer) and start processing it (Start).
Toggle switch
The mode selector is a toggle switch which can be used to set the CPU from RUN
to STOP or reset CPU memory.
Total Current
Sum of currents of all output channels of a digital output module.
U
Ungrounded
Without galvanic connection to ground.
Update interrupt
An update inbterrupt can be generated by a DPV1 slave.
The DPV1 responds with a call of OB56. For detailed information on OB56, refer to
the "System Software for S7-300/S7-400 System and Standard Functions"
reference manual.
User Memory
The user memory contains logic blocks and data blocks of the user program. The
user memory can either be intergrated in the CPU or can be plugged in on memory
card or memory submodules. In general, however, the user program is executed
from the work memory (RAM) of the CPU.
User Program
With SIMATIC a difference is made between the operating system of the CPU and
user programs. The latter are generated by means of the STEP 7 programming
software in the possible programming languages (Ladder Logic, Statement List,
Function Block Diagram) and are stored in logic blocks. Data are stored in data
blocks.
Automation System S7-400 Hardware and Installation
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Glossary
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