which it filters in software to calculate RPM. The 1° signal is also used to determine if the engine is running or has started cranking (to provide faster engine starts). The stock ECU has a co-processor (Hitachi HD6314 Universal Pulse Processor) to handle the pulsed I/Os such as the CAS signal input. The co-processor counts the interval between CAS pulses and the main processor uses that number to calculate the actual RPM with a resolution of +/- 12.5RPM. Since the ECU clock runs at 4mhz, the co-processor has no problem counting the interval between 1° CAS pulses even at 7000rpm. Here's the specific command used by the co-processor:
- Sam |