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170LNT71000 Devicenet Communication Adapter Network Communication Loss Issue

Goals and Symptoms

The purpose of this resolution is to inform users of Momentum 170LNT71000 Devicenet Communication Adapters of an issue with firmware version 1.21.

Facts and Changes

If operating for more than 30 seconds after the network becomes active, bidirectional discrete base outputs can freeze at last value when the LNT DeviceNet adapter loses fieldbus communication.
The issue will occur if a Devicenet Comm Adapter version 1.21 is mounted on a bi-directional module and both Polled and Strobed modes are selected at the same time in the Devicenet Scanner ‘IO Parameters’.

Conditions for this to happen are:

1) the fieldbus connector is removed from the LNT
2) the head PLC is set from RUN to STOP
3) the fieldbus cable power source is turned off

If the conditions occur within 30 seconds of the fieldbus becoming active, bi-directional module outputs will go to zero.

There is no issue when the LNT is mounted on an output module.

Causes and Fixes

At this time, a workaround to this problem involves selecting only POLLED mode in the Devicenet Scanner when using bi-directional modules.

Devicenet Communication Adapters that have firmware version 1.21 installed are:

    • 170LNT71000 communication adapters labeled SV 1.21.
    • 170LNT71000’s labeled SV 1.20 and built after October 2005.

      Adapters built before October 2005 labeled SV 1.20, have version v1.20 installed and are not affected by this issue.
RSNetworks Scanner software can be used to verify the firmware version installed in the Devicenet Communication Adapter. This software reads the SV values in the 170LNT71000 firmware as 1. 011 (SV: 1.20) or 1. 021 (SV: 1.20 or SV: 1.21).

This issue is under investigation by Engineering and is expected to be resolved in a firmware update. An update to this Resolution will be available when new information is provided.
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