Re: Ortonview PCB
After adding the decoupling capacitors the noise on the supply was almost gone, but it was still quite clearly visible on the NENIN output from the PIC. The noise coincided with the switching of the two groups of address pins and my guess is that the drive of the address lines is pulling the supply line inside the PIC, and we can’t get the decoupling any closer to that point. The PIC outputs are strong drivers with fast transition times, so when they drive the address lines to overcome bus capacitance they will pull quite a high current peak from the supply. Series resistors would slow down the transition times and reduce the peak current. This is all just guesswork of course, but was one of my concerns about adding capacitors on the address bus.
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