Knowledge Base

MS120: Onboard counter type A (OBCA)

The controller incorporates an onboard counter type A (called OBCA). This is a high speed hardware counter that can be used for frequency or totalized counting. Typical applications include mains (line voltage) frequency measurement, engine RPM, belt speed (using a pulse encoder) or liquid flow measurement using a turbine flow sensor.

The OBCA exists on several SPLat boards. Generic documentation for the feature is provided in the Onboard counter type A guide.

The OBCA is connected to input number 7. On the MS120 there is no input filtering to limit the maximum count frequency. The maximum count frequency, assuming a squarewave input, is approximately 100kHz. The accuracy is approximately 2% (this varies from product to product, depending on whether they use a crystal for timing or not. This board does not have a crystal).