CL-NET network, COM-LINK
serial connection
340
1SVC 440 795 M1100
Operation of the COM-LINK connection
The active station on the COM-LINK must be in RUN mode.
Data is only exchanged when the active station is in RUN
mode.
The remote station can be in either RUN or STOP mode.
The active station polls the remote station continuously. The
entire READ marker range is transferred as a string. The
entire WRITE marker range is transferred as a string.
Sign of life detection COM-LINK, diagnostics contact ID09
The diagnostics contact ID09 is provided on the active
station of the COM-LINK connection to determine whether it
is functioning properly.
h
Data consistency
The data is located in the image range (data area storing
the marker states) of the active station (1MD..) as well as
in the image range of the remote station (MD..).
Each station writes data to its own image range
asynchronously for data communication. As the serial
interface transfers large data volumes slower than the
devices overwrite the image ranges, the following applies:
one marker double word 1MD…, MD… is consistent.
Within one program cycle, a marker double word that is
written via COM-LINK is not constant. The data via the
COM-LINK is written to the status image over the course
of the program cycle. This means that a different marker
value can be present at the start of the program cycle to
after the write operation via COM-LINK.
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