METHOD AND APPARATUS FOR ANTI-LOCK BRAKE SINGLE CHANNEL WHEEL SPEED PROCESSING WITH DIAGNOSIS

A system for anti-lock brake and traction control has a controller circuit comprising a microprocessor on a silicon die. Inputs from several variable reluctance wheel speed sensors are multiplexed to a single channel on the same die for signal processing including diagnostics, A/D conversion, square wave generation for each sensor by a state machine, and wheel speed determination from the square waves. The diagnostics include detecting sensor and harness short and open circuits by comparison of signals to programmable thresholds and fault timing and latching by gauging open and short signals against programmable time limits. Common mode noise rejection is accomplished by detecting common mode aberration and disabling an A/D converter during the aberrations. Other diagnostics include inputting known artificial signals at sensor inputs or wheel speed circuit inputs and checking for expected outputs, or by calculating wheel speed in parallel paths having the same square wave inputs and using different algorithms.