This fault code (Program Fault) indicates an array index out of bounds or a divide by zero. Ironically, Code 16 is notorious in v16 because the error handling routines in firmware 16.x are less forgiving than v19+.
At its core, the ControlLogix processor uses a 32-bit word length. When you create a DINT (Double Integer) tag, it consumes 32 bits of memory. However, many field devices—such as older analog I/O modules, encoders, and third-party drives—communicate using 16-bit registers. Furthermore, common communication protocols like Modbus TCP/IP or DF1 master-slave often exchange data in 16-bit chunks (registers). Directly mapping a 32-bit tag to a 16-bit device can lead to misalignment, sign errors, or truncated values. RSLogix 5000 bridges this gap through specific data types and explicit programming techniques. rslogix 5000 16
The most common encounter with 16-bit data is during analog I/O processing. A typical 16-bit analog input module (e.g., 1756-IF8) returns a raw value between 0 and 65535 (unsigned) or -32768 to +32767 (signed). RSLogix 5000 reads this into an INT tag. The engineer then converts this 16-bit raw count to engineering units (e.g., 0-100 PSI) using a Compute (CPT) instruction, but must carefully manage the intermediate calculations to avoid overflow because the CPT will operate in 32-bit space. This fault code (Program Fault) indicates an array