Effect of using P2[4] for digital signals on AGND

Question: What is the effect of using P2[4] for digital signals on AGND on PSoC 1?

 

Answer:

Avoid using P2[4] for any digital signals, when using an analog resource depending on the Analog Reference. When P2[4] is used for digital signals, on each +ve and -ve transition of the signal, a spike is introduced into the AGND.  This is because of the coupling effect introduced by the internal capacitance of the AGND Bypass switch.