Thread: Ortonview PCB
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Old 14th Sep 2021, 10:35 pm   #505
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,104
Default Re: Ortonview PCB

Originally Posted by Mark1960 View Post
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 canít 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.
Ah, that makes some sense. I could try that fairly easily by using resistors in place of the links I have instead of buffers.
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