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How to set the input filter in MPC57xx eTimer

Question asked by richard sha on Jun 22, 2017
Latest reply on Jun 27, 2017 by Petr Stancik

Hello,

MPC57xx etimer has input filter configuration by Channel n Input Filter Register (ETIMER_CHn_FILT), the latency is defined (((FILT_CNT + 3) * FILT_PER) + 2) peripheral clock periods.

The question to find the eTimer input filter calculation is not correclty, we set as :

FILT_CNT = 7;

FILT_PER =255;

MOTC_CLK = 16MHz;

the latency is (((7+3)*255)+2)*1/16MHz = 0,1595ms. but I tested result is about 0,42ms(2,38Khz), that mean  signal frequcye over 2,38KHz will be filtered, there are too much gap between 0.1595ms and 0.42ms. Could you help check my calculation if is correct? and how to set and calculate the lantency time period correctlly.

Thank you.

Richard

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