I/O Terminal /
ERROR HANDLING AND DIAGNOSIS
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Digital terminal diagnosis
By default, the diagnostic bits for the digital terminals that have diagnosis are transmitted
cyclically in the process image. These terminals occupy 4 bits each in both the input and
output data. If terminal diagnosis is active, then UserPrmData can be used to specify that
only the I/O data for the digital terminals with diagnosis is to be included in the cyclic process
image transfer:
Byte
Bit
Value
Description
7
4
1
bin
Diagnostic data of digital terminals
not in the cyclic process image
Real-time capacity of the diagnostic data
When making use of terminal diagnosis, it should always be borne in mind that the diagnostic
data always reaches the controller at least one cycle later, and that as a rule access also
takes place through different mechanisms from those used for cyclic process data. This
means that process data can already be faulty, but the controller program is only informed of
this in the following cycle or the one after that. If the diagnostic bits of digital terminals with
diagnosis, or the status of complex terminals, is mapped into the process image, then the
controller program always has consistency between the process data and the diagnostic
data. The appropriate setting therefore depends on the way that the diagnosis is to be used.
If it is only intended for diagnostic display, transmission within the cyclic process data is
unnecessary, but if on the other hand consistency between the process data and the
diagnostic data is desired, then the diagnostic data should be transmitted along with the
cyclic process data.
Maximum diagnosis data length
If more terminal diagnosis data is present than is specified in the maximum diagnostic data
length, then the ExtDiagOverflow bit is set in the standard diagnostic data. Because older
controllers have difficulties with the maximum diagnostic data length of 64 bytes (which is the
default setting), the maximum diagnostic data length can be restricted in the UserPrmData:
Byte
Bit
Description
11
3-6
Maximum length of the diagnostic data. Allowed values:
16, 24, 32, 40, 48, 56, 64
It is only possible to set the maximum diagnostic data length in text form in the extended GSE
file.