Reading multiple ADC channels in FIFO mode

laonia — Mon, 16 May 2022 21:01:03 GMT

Hi,

I'm trying to read ADC values from channels 6,7,12, and 13, but somehow ADC_R returns the same values for all depth. Below are my code:

SIM_SCGC |= SIM_SCGC_ADC_MASK; /* Enable bus clock in ADC*/ ADC_APCTL1 = ADC_APCTL1_ADPC(1<<6) | ADC_APCTL1_ADPC(1<<7) | ADC_APCTL1_ADPC(1<<12)| ADC_APCTL1_ADPC(1<<13); /* Channel selection */ ADC_SC3 = ADC_SC3_ADICLK(0x01) | /* Bus clock divided by 2 */ ADC_SC3_MODE(0b10) | /* 12 bit mode operation */ ADC_SC3_ADLPC_MASK | /* Low power configuration */ ADC_SC3_ADIV(0b11); /* Divide ration = 4, and clock rate = Input clock ÷ 8 */ ADC_SC2 = 0x00; /* Software trigger selected */ ADC_SC4 = ADC_SC4_AFDEP(0b011); /* 4-level FIFO is enabled */ ADC_SC1 = ADC_SC1_ADCH(0x00); /* dummy the 1st channel */ ADC_SC1 = ADC_SC1_ADCH(0x01); /* dummy the 2nd channel */ ADC_SC1 = ADC_SC1_ADCH(0x02); /* dummy the 3rd channel */ ADC_SC1 = ADC_SC1_AIEN_MASK | ADC_SC1_ADCH(0x03); /* dummy the 4th channel and start conversion */

The following code outputs buffer = {4095, 4095, 4095, 4095} when channel 13 is connected to 5V

ADC_SC1 = ADC_SC1_ADCH(0x06); ADC_SC1 = ADC_SC1_ADCH(0x07); ADC_SC1 = ADC_SC1_ADCH(0x0C); ADC_SC1 = ADC_SC1_ADCH(0x0D); while(!(ADC_SC1 & ADC_SC1_COCO_MASK)); buffer[0]=ADC_R; buffer[1]=ADC_R; buffer[2]=ADC_R; buffer[3]=ADC_R;

The following code outputs ADC values in the correct sequence

ADC_SC1 = ADC_SC1_ADCH(0x06); while(!(ADC_SC1 & ADC_SC1_COCO_MASK)); buffer[0]=ADC_R; ADC_SC1 = ADC_SC1_ADCH(0x07); while(!(ADC_SC1 & ADC_SC1_COCO_MASK)); buffer[1]=ADC_R; ADC_SC1 = ADC_SC1_ADCH(0x0C); while(!(ADC_SC1 & ADC_SC1_COCO_MASK)); buffer[2]=ADC_R; ADC_SC1 = ADC_SC1_ADCH(0x0D); while(!(ADC_SC1 & ADC_SC1_COCO_MASK)); buffer[3]=ADC_R;

I though FIFO is supposed to read channels in sequence, but since the four sequential ADC_R all read the same values, I'm guessing my code are reading the same channels four times. I would like to have the ADC configured so that FIFO reads four separate channels when triggered. Is there any configuration or clocking problem with my setup?

Thanks

Re: Reading multiple ADC channels in FIFO mode

Robin_Shen — Wed, 18 May 2022 02:33:39 GMT

Hi laonia,

Seems that you are using KEA MCU. Please refer the example FRDM_KEA128_ADC_FIFO of FRDM-KEAZ Freedom Evaluation Board – QSP.

Best Regards,
Robin
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topic Reading multiple ADC channels in FIFO mode in Kinetis Microcontrollers

Reading multiple ADC channels in FIFO mode

Re: Reading multiple ADC channels in FIFO mode