topic MCF5211/5213 ADC reference selection. in ColdFire/68K Microcontrollers and Processors

MCF5211/5213 ADC reference selection.

foreigner — Tue, 24 Apr 2007 00:27:13 GMT

I have an ADC related question that I would like to get some info on.

I would like to use the VH and VL pins as the reference input on my 5211.

In the MCF5213RM document it indicates that clearing "SEL_VREFH" and "SEL_VREFL" in the "CAL" register selects internal VRx. I just want to make sure that this is the actual VRH and VRL pins and not VDDA and VSSA. When looking at the CF Init utility it indicates setting the bit selects Vrefh and Vrefl pins and clearing the bits selects VDDA and VSSA.

What's the correct answer?

Thanks,

Nick

Re: MCF5211/5213 ADC reference selection.

macl — Mon, 30 Apr 2007 23:12:01 GMT

Hi Nick,

The default condition (SEL_VREFH/SEL_VREFL cleared) is for the reference signals to come from the VRH & VRL pins. The other option is for the references to come from the AN2/AN6 pins. On a previous device (with same ADC), the internal VREFH/VREFL signals were generated from VDDA/VSSA because there were no external VRH/VRL pins. That's why you are able to get the signals from AN2/AN6 as a second option. On this device however, there are VRH/VRL pins so the documentation is a little confusing.

Thanks,

Mac