Functional Restrictions And Limits - WAGO -I/O-SYSTEM 750 Manual

WAGO-I/O-SYSTEM 750
750-882 Media Redundancy ETHERNET Controller
9.3

Functional Restrictions and Limits

The basis of WAGO-I/O-PRO, the standard programming system CoDeSys by
3S, has an integrated visualization. Dependend on the target, this visualization
can be used in the variants "HMI", "TargetVisu" and "WebVisu".
The fieldbus controller supports the process variants "HMI" and "WebVisu".
Depending on the version, there are technological limitations.
Several options for complex visualization objects "Alarm" and "Trend" are only
provided by the "HMI" version. This applies, for example, to sending emails as a
response to an alarm or for navigating through and generating historical trend
data.
Compared with "HMI", the "WebVisu" on the fieldbus controller is executed within
considerably tighter physical limits. Whereas the "HMI" can call upon the
resources of a PC, the "WebVisu" operate within the following restrictions:
File system (2 MB):
The overall size of the PLC program, visualization files, bitmaps, log files,
configuration files, etc. must fit into the file system.
The PLC browser delivers the amount of free disk space in response to the
command "fds" (FreeDiscSpace).
Process data buffer (16 kB):
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 ("|") separates two process values. For this reason,
the required space of a process data variable in the process data buffer not only
depends on the data type, but also on the process values itself. A "WORD"
variable therefore occupies between one byte for the values 0...9 and five bytes
for values greater than 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 number of modules (1023/default):
The total size of the PLC program is determined, among other things, by the
maximum number of modules. This value can be configured in the target system
settings.
Computing power/processor time:
The 750-882 is based on a real-time operating system with pre-emptive
multitasking. High-priority processes such as the PLC program will eliminate low-
priority processes.
The web server supplies process data and applets for the web visualization.
Make sure when configuring tasks, that there is sufficient processor time
available for all processes. The "freewheeling" task call option is not suitable in
conjunction with the "WebVisu"; as in this case, the high-priority PLC program
suppresses the web server. Instead of this, use the "cyclic" task call option with a
realistic value.
Programming the PFC Using WAGO-I/O-PRO 135
Manual
1.5.0