Hello,

I am on the learning curve with the 8051/52 be kind ;-). I am using external INT4 to capture a pulsed input that represents RPM on an engine. I am getting an error that is linear with frequency but I am not sure what is causing it. The Infineon C515 is running at 12 Mhz and should be more than fast enough for my needs.

The error is as follows, I am using an external freq counter as my reference. The error looks like dropped pulses but I am not sure. I am feeding it a 50% duty cycle wave at the moment.

6000 Hz - 420 Hz error

3000 Hz - 210 Hz error

1500 Hz - 105 Hz error

and so on. If this rings any bells for someone I would appreciate any pointers.

Thanks,
Dennis G.