ICK. I have an 18f26K22 onboard on a new circuit. Fortunately most of the=20 sources are low-impedance, but I have one which is a voltage divider. =20 Final rev of the board is going out in the next day or so I'm glad you=20 mentioned this.. What is darn frustrating is if you look at page 302 in the datasheet (=20 http://ww1.microchip.com/downloads/en/DeviceDoc/41412D.pdf ), it says=20 'The maximum recommended impedance for analog sources is 10K'. And I know very well I went through this page during=20 engineering. The 10K figure is even repeated in the footnote on this=20 page. Since this basically measuring the voltage source to the board, and=20 shouldn't be changing (that fast), I'm just going to add a .1uF ceramic=20 cap at the input pin. Assuming the values are close in figure 17-5, a=20 ..1uF cap should have plenty of 'storage' to be able to provide an=20 effective low-impedance source to the PIC. I would be a bit more picky=20 if this was a critical measurement instead of a nicety... But=20 considering it needs the low impedance source only a relatively small=20 percentage of the time, it should be ok... -forrest On 9/2/2011 9:44 PM, PICdude wrote: > Heard back from FAE. Seems like there is a process change on the > 18F's, so the spec really has changed. Sucks. But that allows for > quite fast acquisition times, which I don't need, so hopefully the > longer charge-time I'll use will still be fast enough to get the > sample rate I need. I need to read the specs in detail and run some > tests. > > > > Quoting PICdude: > >> Some time ago I started porting to an enhanced PIC 16F1936 to replace >> 16F883's I've been using, so I could get a faster internal osc and >> touch-switch capability. But there are some annoyances (bugs which >> have unpleasant workarounds in the errata). But now there's a >> 18F23K22 that I'm thinking I'll use instead. Same package& pinout >> (so boards don't change), no banking, faster (in case I need it), and >> no Vcap, so I'll get that pin back. >> >> However, I notice that the Zain (min recommended analog source >> impedance) on the 18F is 3k, vs. 10k on the 16F. And the 18F does not >> state that higher is okay with a 0.01uf cap as with the 16F. Why is >> this? Did something change, or did they re-think the specs on the >> same module, or...? I've been using sources with over 20k impedance >> with no problems, but with a much longer sample-cap charge time. Is >> there some reason I won't be able to do this with the 18F part? >> >> Cheers, >> -Neil >> >> -- >> http://www.piclist.com PIC/SX FAQ& list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .