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Resolved - TOP Server V5.14.491.0 Modbus TCP Ethernet Driver Block Size Issue

I'm using TOP Server V5.14.491.0, specifically the Modbus TCP Ethernet driver. I am seeing "Attempt to add item failed" errors in my TOP Server event log even though I have confirmed the tag/address is valid. What might the issue be?

We have been made aware of an issue that was introduced as part of the new CEG device model enhancement made in the Modbus Ethernet driver for TOP Server V5.14.491.0. The issue affects users with smaller Block Size settings in the device properties.

This issue was resolved in V5.14.493.0 (V5.14 R2) or higher - click here to request version 5.14.493.0.

Users are STRONGLY recommended to download the latest version of TOP Server for their supported operating system.

Problem Details:

For Holding Registers and Internal Registers, the issue is present with block sizes of 1 through 4 and for Input and Output Coils, the issue is present with a block size of 8.
This results in one of the following occurring:

  • the tag/address will not be added at all when the client application requests it, resulting in an error message in TOP Server of "Attempt to add item 'Item Reference' failed"
  • an invalid request will be sent to the device, resulting in a Modbus exception response and bad quality data.

Which of those two scenarios you might see will depend on how many total Modbus addresses your clients are requesting and what the data types are, specifically 32- or 64-bit addresses for registers will display these issues.