Siemens SIMATIC PCS 7 CPU 410-5H System Manual page 81

During the discrepancy time, the most recent matching (non-discrepant) value is written to
the process image of the module with the lower address. This procedure is repeated until the
values once again match within the discrepancy time or until the discrepancy time of a bit
has expired.
If the discrepancy continues past the expiration of the configured discrepancy time, an error
has occurred.
The defective side is localized according to the following strategy:
1. During the discrepancy time, the most recent matching value is retained as the result.
2. Once the discrepancy time has expired, the following error message is displayed:
Error code 7960: "Redundant I/O: discrepancy time at digital input expired, error not yet
localized". Passivation is not performed and no entry is made in the static error image.
Until the next signal change occurs, the configured response is performed after the
discrepancy time expires.
3. If another signal change now occurs, the channel in which the signal change occurred is
the intact channel and the other channel is passivated.
Note
The time that the system actually needs to determine a discrepancy depends on various
factors: bus runtimes, cycle and call times of the user program, conversion times, etc.
Redundant input signals can therefore be different for a longer period than the configured
discrepancy time.
Modules with diagnostics capability are also passivated by calling OB 82.
MTA Terminal Modules
MTA terminal modules (Marshalled Termination Assemblies) can be used to connect field
devices, sensors and actuators to the I/O modules of the ET 200M remote I/O stations
simply, quickly and reliably. They can be used to significantly reduce the costs and required
work for cabling and commissioning, and prevent wiring errors.
The individual MTA terminal modules are each tailored to specific I/O modules from the
ET 200M range. MTA versions for standard I/O modules are also available, as for redundant
and safety-related I/O modules. The MTA terminal modules are connected to the I/O
modules using 3 m or 8 m long preassembled cables.
Details on combinable ET 200M modules and suitable connection cables as well as the
current MTA product range are available at this address: Update and expansion of the MTA
terminal modules (http://support.automation.siemens.com/WW/view/en/29289048)
CPU 410-5H Process Automation
System Manual, 09/2014, A5E31622160-AB
4.7 Connecting redundant I/O to the PROFIBUS DP interface
I/O configuration variants
81