There is usually no hardware exclusively devoted to the OBCA function. Basically, the OBCA comes “free” in the design of the SPLat board. On some custom boards, however, the OBCA may be associated with special purpose input conditioning circuitry. An example of that would be a variable reluctance (often referred to a VR or reluctor) proximity pickup interface, as you might use to detect engine rpm off the flywheel of a diesel engine.

That said, the OBCA operates in conjunction with a hardware input. Usually this is simply a regular input that can be used for counting via the OBCA or as a normal input. The theoretical maximum is 650kHz, as determined by the shortest timebase and the count capacity. The actual maximum count frequency on a given SPLat board will depend on any hardware input filtering on the input in question, and will typically be 15-30kHz. Please see your product specific documentation for more information.