Using P2[4] as AGND with AGNDBYPASS

Question: Can I use P2[4] as AGND by enabling the AGNDBYPASS parameter?

 

Answer:

There is an internal 8.1K resistor between P2[4] and the internal AGND.  This 8.1K along with the external bypass capacitor forms a Low Pass Filter that filters any noise on AGND.  Because of this high value of internal resistance, it is not adviceable to use P2[4] as a reference AGND for any analog system.  The best way to bring out AGND is by using a RefMux user module or by writing to testmux bits in the ACBxxCR2 register and through an analog output buffer.  The analog output buffer is a low impedance source and will provide a stable AGND.  When using P2[4] as AGND reference, an external OpAmp buffer needs to be placed at P2[4] to get low impedance AGND reference source.