Knowledge Base / Rockwell In-chassis

Array Subscript too Large Controller Fault

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The ladder logic that handles the module's operation makes an assumption that the size of the ReadData and WriteData blocks are at least one block transfer wide. So, for example, if you are using a block transfer size of 240, but the ReadData and/or WriteData arrays are set to a length of 230, the controller will fault with this error.

The fix is fairly simple: First, in Prosoft Configuration Builder, set the Read Register and Write Register counts to at least the size of a single block transfer (could be 240, 120, or 60). Next, in your Logix program, browse to the User-defined data types in the Controller organizer. Search for the MBSDATA, MBTCPDATA, MCMDATA, etc user-defined type (depends on the specific module being used), and modify the data type so that the size of the ReadData and WriteData arrays match the register counts specified in Prosoft Configuration Builder.