We would like to draw your attention to an issue which has been reported to SCADA Global Support regarding the Modnet communication driver.
The issue was reported on Modnet Driver version 2.6.19.0 (release), but is likely to exist on all versions of the driver and is fixed in Modnet Driver version 2.06.025.001 (release).

The issue is independent of the version of SCADA.
The issue has so far only been noted when communicating with Unity Quantum PLCs.

Symptoms:

The Modnet driver allows users to write to individual bits in a word using a process known as "read modify write".
Under certain circumstances other bits in the word being written to can be affected in a random manner.

Circumstances:

The issue only occurs when using the write to bit in a word as described above; other write operations are not affected.

For example, writing to addresses such as 400007.3 or %MW500.5

The issue can only occur when the following parameters are used in the CITECT.INI file:

[Modnet] MaxPending greater than 1
and
[Modnet] MaxOutstanding greater than 1

Please note: the default installed values of these parameters in the current version of the driver are:

[Modnet] MaxPending = 2
[Modnet] MaxOutstanding = 1

Older versions have higher values for both parameters.
Only devices capable of processing requests out of order can demonstrate this issue.
The issue only occurs under increased load conditions when multiple requests are likely to be processed out of order.

Workaround:

This issue can be avoided by setting the following parameter to be used in the CITECT.INI file:

[Modnet] MaxOutstanding = 1

Note that this workaround can result in a degradation of the communications performance to the Modnet device(s) if you have higher values for this parameter.

Solution:

This problem is rectified in the Modnet Release version 2.06.25.001. 
Download from DriverWeb and Install.

If you want to receive updates on Modnet driver notifications and discussions you may subscribe to the Modnet forum of DriverWeb or check our website for updated information.

For assistance:

• Vijeo Citect customers, contact your local Schneider office.

• CitectSCADA and CitectFacilities customers, contact the SCADA Global Support Centre on the appropriate number for your country listed below.

SCADA Global Support Centre contact details: 

OCEANIA
Australia: 1300 131 631
New Zealand: 0800 880 026

AFRICA
South Africa: 0800 998 887

LATIN AMERICA
Brazil: 800 891 2162
Mexico: 001 866 522 0285

MIDDLE EAST
Israel: 1 809 216 065

NORTH AMERICA
USA/Canada: 866 589 6855

GREATER CHINA
China: 10 800 712 1587

NORTH ASIA
Japan: 00531 121 985
South Korea: 00798 14 800 7112

SOUTH EAST ASIA
Singapore: 0800 120 4562

EUROPE
Belgium 0800 40 710
Czech Republic 0800 134 466
Denmark 808 87 453
Finland 0800 913 065
France 04 72 15 84 50
Germany: +49 8931901445
Hungary: 06 800 18490
Italy: 800 986 902
Norway: 800 11979
Spain: 800 098 944
Sweden: 0200 882 612
Switzerland: 0800 001 241
Netherlands: 0800 020 0498
UK: 0800 376 2869 

ALL OTHER COUNTRIES
Reverse call charges: +61 2 9496 7400

EMAIL
support@citect.com