On Wed, Jun 24, 2009 at 6:57 AM, solarwind wrote: > On Wed, Jun 24, 2009 at 5:25 AM, Russell McMahon wrote: >> Very simple - yes. >> Operating - sometimes, maybe, depending on assumptions which may have been >> made but which are not shown on the diagram. >> >> Not showing all assumptions made makes it hard for people to provide useful >> comment. (Putting SOME of them in an added list is a good start but showing >> them on the circuit even better). >> >> Re other query re capacitor size - you need to read the reasonably extensive >> prior discussions on decoupling capacitors or look at a good web reference, >> of which there will be thousands. The "how big should a capacitor be" >> question is often asked and almost as often answered. Having somebody tell >> you it's not too crucial (it's not) is not a substitute for looking around >> at what is done and learning why. As 'another list member' pointed out >> recently, lack of understanding and proper treatment of decoupling >> capacitors is a major source of probelms. I don't think he put it quite that >> way :-).And, more caps often don't hurt. Avdd to Avss may benefit from such. >> or may not, sometiomes. >> >> Hardware terminating /MCLR in any of the several approved manners is >> generally held to be superior to disabling it in software, where that is an >> option. (Where it's not an option then doing it in hardware is a *REALLY* >> good idea :-) ). >> >> With such a capable device it would be usual to use an external crystal or >> clock source. ie if you are using a DSPIC then it won't be long before you >> would like the clock frequency to be moderately accurately known and stable. >> Providing for a crystal and not using it at first works better than not >> providing for it and wanting to use one. >> >> Diagram and reality never correlate 100% but note that it may be better to >> run all ground traces directly to the common ground point than to chain them >> as shown. AVss especially is provided separately for good reason. This being >> a dsPIC you may care more in this case than in many others. Ground currents >> flowing in the common ground path will appear as signal to the analog >> circuitry if built as shown. Gargoyle knows all about this. For many >> applications this may not make a vast difference but as it's as easy to do >> right as wrong you might as well get in the habit of doing it pedantically >> against the day when you need to care. >> >> You may wish to group some ISP pins on a header. >> >> Beyong minimalist, but you MAY want to provide options for SIP resistor >> packs of high resistance pull up/downs for some pins to make the software >> rogours less demanding. If you are well disciplined at ensuring the software >> matches the hardwrae (nothing floats without a pull [up|down], all >> unterminated pins are outputs, analog functions are disabled when not used >> and allowed for appropriately in hardware, ...]. >> >> ie it's just another processor and indeed just another IC whose pins must be >> terminated correctly as per spec sheet - but it has a bit wider definition >> of "correctly" than say a 74HC14 (gotta love those Schmitt imputs). > > Wow - I just want it to work :( > > For my PIC18F2620, all I did is hook up ICSP pins, UART pins, a > decoupling cap and it worked. I'm asking (in a similar fashion) how to > quickstart with the dsPIC with minimal fuss and minimal components. > That is, other than 3 caps, would anything else be REQUIRED to get it > up and running? (I have PICKIT2 hooked up to ICSP and UART lines to > MAX233A) > > I ask because I see all these new pins (AVSS, AVDD, VDDCORE) that I > don't really know what to do with... Sure, there's the datasheet, but > it's so BIG, that it's easy to miss something. Also, for such a simple > quickstart circuit, I was hoping someone could provide, short, concise > answers. It shouldn't be too much of a problem since the circuit IS > simple and it's just to get started (program hello world code and see > it on my terminal). > Don't get me wrong, your long, detailed explanation is much appreciated, but for someone who's diving into a very different chip for the first time, it can be overwhelming. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist