BECKHOFF BK3xx0 - Manual (Page 74)

Notes on the Documentation
72 Fieldbus Components
Terminal Diagnostics
If terminal diagnosis has been activated, then each channel of a complex terminals is examined to see whether bit 6
in the status has changed (exceptions are the KL6001, KL6011 and KL6021, where the relevant bit is bit 3), and
whether the diagnostic bit of each channel of a digital terminal with diagnostics (KL12x2 or KL22x2) has changed. If
that is the case, the existence of new diagnostic data is reported to the master, and two bytes of diagnostic
information starting at byte 16 of each channel for which a diagnosis is pending are inserted (see Diagnostic data).
Terminal diagnosis can be activated in the UserPrmData:
Byte Bit Value Description
7 1 1
bin
Terminal diagnosis is active
Digital terminal diagnosis
By default, the diagnostic bits for the digital terminals that have diagnosis (KL12x2 and KL22x2) 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 (KL12x2: 2 bit inputs, KL22x2: 4 bit outputs) 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 GSD file.