Operation of I/O in a safe system

A module health system includes a module health circuit comprising a hardware register that is set to a first value in response to the system starting, an application register that is set to the first value in response to the system starting and a watchdog timer register that is set to the first value in response to the system starting. The system further includes a power on self-test that determines whether the system has passed a plurality of tests and that selectively sets the hardware register to a second value based on the determination, an external software application that determines whether a safety critical system is healthy and selectively sets the application register based on the determination, a watchdog timer application that selectively sets the watchdog timer register, a central processing unit that determines whether to de-assert a module health signal.