topic Strange behaviour in DSC´s ADC12 in Digital Signal Controllers

Strange behaviour in DSC´s ADC12

cabl — Wed, 04 Feb 2015 15:18:53 GMT

Hi everybody,

I´m using DSC56F84789 + CW10.4 + ProcessorExpert to develop a project that samples several channels of the ADC12 (triggered parallel, converter A only, simultaneous). I can see random samples that are close to (or exactly at) 16384, when the sampled signal is a sinusoidal ranged from +5000 to -5000, 50 Hz which a sampling frequency of 6400 Hz. Sampling is perfet appart from these sporadic (once a day, once in a weekend, twice a day...) outliers.

Has anyone experienced a similar problem?

As I know there´s a bug in PE that generates wrong configuration of ADC, I manually setup up the ADC12 registers like this:


	setRegBit(ADC12_CTRL1,STOP0); //0x4000: Stop command issued

	setRegBit(ADC12_PWR,APD);//Activa autoapagado

	clrRegBits(ADC12_PWR2,ADC12_PWR2_SPEEDA_MASK);	//relojA <5MHz

	setRegBitGroup(ADC12_CTRL1,SMODE,0b101);//0x0005: triggered parallel
	setRegBit(ADC12_CTRL1,EOSIE0);	//0x0800: ADCA EOSI0 interrupt enabled
	setRegBit(ADC12_CTRL1,SYNC0);	//0x1000: ADCA Triggered by SYNC0 pulses

	clrRegBit(ADC12_CTRL2,SIMULT);	//0x0000: Independent

	setRegBitGroup(ADC12_CTRL1,CHNCFG_L,0x03);	//0x0030
	setRegBitGroup(ADC12_CTRL2,CHNCFG_H,0x03);	//0x00B0

clrRegBit(ADC12_CTRL1,STOP0); /* Stop command cleared */

Best regards

Re: Strange behaviour in DSC´s ADC12

xiangjun_rong — Thu, 05 Feb 2015 03:00:43 GMT

Hi, Carlos,

Firstly, all analog channel's allowed voltage are from GND to 3.3V, the analog channel pins ANAx or ANBx can not accept negative voltage from hardware perspective.

Secondly, I suggest you use Simultaneous mode by setting the SIMULT bit in ADC0_CTRL2.

Pls have a try, if there is still have abnormal digital sample, update the community page.

setRegBit(ADC12_CTRL2,SIMULT);//0x0000: simultaneous mode

Xiangjun Rong

Re: Strange behaviour in DSC´s ADC12

cabl — Tue, 10 Feb 2015 10:48:33 GMT

Dear Xiangjun,

thank you very much for the answer. However, I can see the point of using simultaneous mode if I´m not sampling any ADCB channels. More over when there are certain issues with ADCs power consumption.

By the way, I´ll give a try to the simultaneous mode.

Re: Strange behaviour in DSC´s ADC12

xiangjun_rong — Fri, 13 Feb 2015 03:04:43 GMT

Hi,Carlos,

what is the result, any progress?

XiangJun Rong

Re: Strange behaviour in DSC´s ADC12

cabl — Fri, 13 Feb 2015 10:34:22 GMT

Dear Xiangjun,

this strange behaviour appears once in a while, so I need days to be sure whether every change takes effect or not.

I´ll keep you informed.

Thanks again.