Controllers with SERCOS and issues reaching phase4 due to improperly configured cable lengths, faulty fiber optic cables were most susceptible to the 0x8F000012 task error. This task error is generated if an IRQ 7 interrupt is generated when not expected.

IRQ7 is the receive interrupt that is generated by the DSP to indicate it has response data ready.

This bug could readily be duplicated by tying the receive and transmit SERCOS ports together with a single fiber optic cable.

The problem was caused by a bug in the controllers Operating System API functions for installing, enabling and disabling interrupt vectors. These functions were allowing interrupts to occur during the function.

Additional restructuring of when Interrupt Vectors were enabled and disabled was done in the SERCOS task.