Redundant I / O links are standard for maximum security. Alternatively, advanced analog input, intelligent transmitter interface, analog output, digital input and digital output processors may be redundant. I / O processing and control processing functions are carried out separately, so I / O scanning rate is completely independent of I / O quantity, controller load, processing and alarm. This functional partitioning allows more efficient use of advanced control processor functions and provides future I / O expansion.Any combination of the above I / O processors can be selected for PM / APM / HPM / ehpm controllers. This can be any combination of single and / or redundant (HLA, STI, Ao, Di and do) pairs, up to 40. Even if a maximum of 80 physical IOPs are supplemented, the control or communication performance will not be affected. In the redundant IOP configuration, control will be automatically transferred to the standby I / O processor during board replacement or failure.Although a separate FTA of a given type is required to handle different field wiring signal levels, the same I / O processor can usually be used. This I / O method simplifies the selection of system hardware and minimizes the demand for spare parts. For example, a digital input processor may process 24 VDC, 120 VAC, 125 VDC, or 240 VAC, depending on the FTA selected.