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Frequenz messung

Question asked by bernd korndörfer on Sep 4, 2018
Latest reply on Oct 4, 2018 by bernd korndörfer

My goal is to measure a sensor frequency in between 50kHz to 120kHz for a high resolution. As the first step I want to divide this frequency to be able for handle on the LPC111x.

Therefore I am using that signal as an external input on PIO3_5 to the Timer/counter using the Timer/Counter setup:

LPC_IOCON->PIO3_5     = (LPC_IOCON->PIO3_5 & ~(0x3FF)) | 0x21;  //set up pin (sec 7.4.17)  (no pull up, Hyst enable)

 LPC_SYSCON->SYSAHBCLKCTRL |= (1<<7)|(1<<16)|(1<<6);  //enable clock signal CT16B0 (sec 3.5.14)                                                

LPC_TMR16B0 ->PR                         = 0;               //no preclear (sec 18.7.4)

LPC_TMR16B0 ->MR0 = 200;         //compare-counter(sec 18.7.7)

LPC_TMR16B0 ->MR1 = 0;         

LPC_TMR16B0 ->MCR = 0x03;        //TC Reset on MR0 Match, enable Interrupt (sec 18.7.6)

 LPC_TMR16B0->EMR  = 0x30;      //do nothing (sec 18.7.10)

LPC_TMR16B0 ->PWMC = 0;        //no PWM Mode, (sec 18.7.12)

LPC_TMR16B0 ->CTCR = 05;                            // (sec 18.7.11)          counter mode on rising edge, CT16Bn_CAP0

LPC_TMR16B0 ->TCR                        = 02;          //reset (sec 18.7.2)                   

LPC_TMR16B0 ->TCR                        = 01;          //GO (sec 18.7.2)


For the first test I am reading in a polling loop the  LPC_TMR16B0->TC and expecting random values, but getting just zero.

I am not going to use the Capture.

May be I am not understanding some basics in using the external Counter input.