On Thu, Jun 25, 2009 at 11:45 PM, peter green wrote: > Most likely to act in combination with the decoupling capacitor as a > power supply filter for the analog supply. It can probablly be replaced > with a wire if you aren't too concerned about ADC accuracy. > >> 2. Could someone please explain what the circuitry near the MCLR pin >> is doing? Is it just a pullup on the MCLR with a decoupling cap? Or is >> there something else going on? >> > It looks to me like a circuit designed to delay the rise of MCLR to hold > the chip in reset while the power supply comes up and stabalises. Note > that on the other side of that page they reccomend that you make the > capacitor disconnectable and disconnect it for programming/debug purposes. > >> 3. The dsPIC has an internal voltage regulator that regulates voltage >> to its core (I believe). What kind of regulator is it? (ex. linear, >> charge pump based, so on) >> > I can't seem to find a reference in the datasheet but given that the > only external component is a capacitor on it's output it is almost > certainly a linear regulator. >> 4. I'm guessing that the decoupling caps act as mufflers for >> noise/spikes/dips and compensate for abrupt voltage changes. > Their main purpose is to stop current spikes (which are a fact of life > with cmos logic) turning into voltage spikes/dips >> In that >> case, I can see why they are placed in (parallel?) with the power >> lines. However, there is a cap placed in series with the VCAP/VDDCORE >> line. How does this cap behave? What does it do? >> > It is in paralell with the regulator output. The regulator is connected > internally to the core but you have to provide a decoupling capacitor to > ground externally because large capacitors are very difficult/expensive > to integrate in an IC. Thank you for that detailed response to my lengthy question. I understand the circuit a lot better now. I just hooked up everything with a little modification and it all seems to be working as expected. I just need to write some code and load it up now! -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist