Siemens SIMATIC S7-1500 Function Manual page 51

Glossary
Direct access, direct data access
As an alternative to access via the process image, you also have direct read and write
access to the I/O, if this is necessary for programming reasons. A direct (write) I/O access
also writes to the process image. This prevents a subsequent output of the process image
from overwriting the value written by direct access.
Distributed I/O system
System with I/O modules at a distance from the CPU controlling them.
DP master
A master that behaves in accordance with EN 50170, Part 3, is called a DP master.
→ See also Master
DP slave
A slave operated on PROFIBUS with the PROFIBUS DP protocol and in accordance with
EN 50170, Part 3 is called a DP slave.
→ See also Slave
Execution window
The "SYNC_PI" and "SYNC_PO" instructions can update the process image partition only
within the permitted execution window in isochronous mode. The execution window refers to
the time period during which a call of the SYNC_PI and SYNC_PO instructions is possible,
i.e. from the end of the cyclic data exchange until the point in time before the end of data
cycle T_DC at which the outputs can still be transferred to the I/O in time. In STEP 7 the
delay time is preset to the start of the execution window. A violation of the execution window
is signaled by an error message at the block call.
I/O modules
All modules that can be operated with a CPU or an interface module.
I-device
The "I-device" (intelligent IO device) functionality of a CPU allows it to exchange data with an
IO controller and thus to be used as an intelligent preprocessing unit of sub-processes. In its
role as an IO device, the I-device is connected to a "higher-level" IO controller.
Interface module
Module in the distributed I/O system. The interface module connects the distributed I/O
system to the CPU (IO controller) via a fieldbus and processes the data for and from I/O
modules.
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Isochronous mode
Function Manual, 10/2018, A5E43884988-AA