Abnormal period values when using eMIOS IPM mode

[sx]

Hi,

I want to use 5748G to control a pwm fan . And i configured an eMIOS channel as IPM mode to measure the fan's speed. Sadly the period calculated by the IPM seems not quite right. I found someabnormal values, and the longer the period is, the more abnormal values are. So please help me to fix it.

There are some codes from my application:

And there are some results: 

when period = 24000 us

when period = 12000 us

when period = 1000 us

when period = 50 us

[PetrS]

Hi,

the eMIOS contains a 16bit counter on MPC5748G. So if you use 100000 (0x186A0) as boundary for Counter Bus A, then a time base is counting up to 0x86A0 (34464) only.

If you will use 34464 as MAXCNT in your calculation, you got right period values.

BR, Petr 

[sx]

Another question: How can i calculate the period if there are several overflows? Or how can i determine the number of overflows?

[PetrS]

you can enable interrupt for channel 23 and increment some global variable indicating oveflows. Then use this variable value within period calculation.

BR, Petr

[sx]

Ok, thanks for your help!

[sx]

Oh, i forgot this, thanks!