Onboard counter B is a counter implemented in SPLat firmware, so is almost guaranteed of being supported by every controller with digital inputs. Also refer to OBCB generic documentation or OBCA generic documentation for in-depth details.
Here's a table that summarises the difference between the OBCA and OBCB counters and how they are implemented on SPLat 8bit controllers and SPLat 32bit controllers:
| Number of Inputs | Ideal Max Speed | |||
|---|---|---|---|---|
| Controller Type | 8bit | 32bit | 8bit | 32bit |
| OBCA | 1 max | Board Dependant | 650kHz | 10+MHz |
| OBCB | 8 max | All Inputs | 2kHz | 2Khz |
For most applications, OBCB is fast enough and is present on many more inputs. In the case of a SPLat 32bit controller, all the digital inputs support OBCB.