>Thanks for the help, I clearly need to learn a lot more about basic electronics theory :/ You are at the right place, Matt! -- Lawrence Lile Matt Marsh Sent by: pic microcontroller discussion list 04/13/2004 04:04 PM Please respond to pic microcontroller discussion list To: PICLIST@MITVMA.MIT.EDU cc: Subject: Re: [PIC:] Capacitor between VDD & VSS ? On Tuesday 13 April 2004 21:54, Byron A Jeff wrote: > On Tue, Apr 13, 2004 at 09:45:10PM +0100, Matt Marsh wrote: > > Hi, > > > > I've seen a number of circuits where a capacitor is placed > > between the VSS and VDD pins of the PIC. > > Of course. > > > Is this something that should always be done? > > Of course! ;-) > > > What is the purpose of this capacitor? > > Bypass capacitor. Some quick cap theory. In short it blocks fixed > DC signals and allows variable signals to pass across the cap. > Clearly the VSS/VDD connection should be as DC as it gets. But in > fact there's a lot of noise on power supply lines that can affect > circuit operation. So one purpose of the bypass cap is to create > a low impeadance path to eliminate noise on the power supply > lines. > > The second item is that many modern circuits that utilize CMOS > technology will draw significant spikes of power when switching. > So at each clock edge you'll get a bit of a voltage dip. Bypass > caps can provide additional power in those dips. > > So in the end bypass caps stabilize your power supply to your > chips reducing the amount of noise on those power supply lines. > > Sprinkle liberally. Thank you! And yes, this is all making sense now along with the article Jan-Erik pointed me at :-) Thanks for the help, I clearly need to learn a lot more about basic electronics theory :/ Matt -- Matt N. Marsh Email: matt@mattmarsh.net Yahoo: marshmn Web: http://www.mattmarsh.net/ Jabber: mattmarsh@jabber.org MSN: matt@mattmarsh.net ICQ: 250467363 AIM: MattMarshUK -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.