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Fieldbus Controller
Fieldbus Controller 750-872/020-000
3.1.8.2 Restrictions in the Function Range
The basic of WAGO-I/O-PRO CAA, the standard programming system
CoDeSys from the company 3S, has three process variants "HMI",
"TargetVisu" and "WebVisu"within the integrated visualisation system.
The 750-872/020-000 Ethernet controller supports the process variants "HMI"
and "WebVisu". There are technological limitations depending on the process
variant.
Different options of the complex visualisation objects "Alarm" and "Trend"
are available exclusively in the "HMI". This applies, for example, for sending
e-mails as a response to an alarm or for navigating through and generating
historical trend data.
On the Ethernet Controller 750-872/020-000 the "WebVisu" is executed
within considerably tighter physical limits, compared with "HMI". Whereas
the "HMI" can call upon the almost unrestricted resources of a PC, the
"WebVisu" must take into account the following restrictions:
File System (1,4 MB)
Process Data Buffer (16 kB)
Number of Modules
(512/default)
Computer Power/Processor
Time
Technological Limitations of the CoDeSys WebVisu
The total size of PLC program, visualisation files, bitmaps,
log files, configuration files etc. must fit into the file system.
The PLC browser returns the free memory available with
the command "fds" (FreeDiscSpace).
The WebVisu uses its own protocol for exchanging process
data between applet and control system.
In doing so, the process data is transmitted with ASCII
coding. The pipe character ("|") is used as a separator
between two process values.
The space required for a process data variable in the process
data buffer is therefore not only dependent on the type of
data but also on the process value itself. A "WORD"
variable therefore occupies between one byte for the values
0... 9 and five bytes for values above 10000.
The selected format allows only a rough estimate of the
space required for the individual process data in the process
data buffer.
If the size is exceeded, the WebVisu no longer works as
expected.
The total size of the PLC program is determined, amongst
other things, by the maximum number of modules. This
value can be configured in the target system settings.
is based on a real-time operating system with pre-emptive
multitasking.
With this system, high-priority processes, such as the PLC
program, for example, interrupt or suppress low-priority
processes.
The web server, which is responsible for supplying the
applet and exchanging process data with the applet, is such a
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP
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