Shawn/ Harold, Thanks so much for the detailed explanations. I will read more about Basic Electronic Theory on the web page you recommended. Cheers, Davis PS: Hv a fantastic weekend !! Harold Hallikainen wrote: OK, I'll jump in here. Just finished teaching a class on digital electronics at Cuesta College, San Luis Obispo, CA. I believe a lot of the terminology is based on conventional current flow (instead of electron current flow), so we assume current flows "down hill" from positive to negative, or from more positive to less positive, etc. Source current is current conventional current leaving the device. For example, if we have a PIC pin that is high (+5V) and load it with 1k to ground, the PIC is sourcing 5mA. Most PIC pins can source 25mA. Sink current is how much current the pin can "sink" or pull down. If, for example, we have a 1k resistor between a pic pin and +5V, and the pin is low (0V), we have 5mA flowing into the pin. The pin is sinking 5mA. Most PIC pins can sink 25mA. An open collector (bipolar transistor) or open drain (FET) output is one that can sink current but not source current. Open drain outputs are often connected in parallel and have a pull-up resistor somewhere. When any of the outputs go low, bus is pulled low. This is often used for interrupt lines. Any device can pull the interrupt request line low. The processor then polls the devices to see which pulled it low. For a little more basic electronic theory, see http://kauko.hallikainen.org/rw/theory/ Good luck! Harold > Ok, I'll take a shot at these. The terminology gets pretty confusing > sometimes. As for the best place to look? Probably an EE book. > > -Sink current is how much current you can sink, or how much you can pass > through that portion of the circuit. > > -Source current is how much current you can source, or how much current > that portion of the circuit can pony up. > > -Open drain means that it goes straight to ground at some point. > Usually sooner than later. :-) . In other words, you would be able to > sink a larger amount of current through that portion of the chip than > one that had a specificed sink current. TYPICALLY. > > Someone jump in if I screwed anything up, but that should be pretty > accurate. > > > Shawn Wilton > Junior in CpE > MicroBiologist > > Phone: (503) 881-2707 > Email: shawn@black9.net > > http://black9.net > > > techy fellow wrote: >> Hi All, >> >> Am new to electronics, can someone kindly explain to me or direct me to >> somewhere I can do my own reading on the following commonly used terms >> for MCU; >> >> - Sink Current >> - Source Current >> - Open Drain >> >> Thanks in advance. >> Davis >> >> >> >> >> --------------------------------- >> Do you Yahoo!? >> Friends. Fun. Try the all-new Yahoo! Messenger >> >> -- >> http://www.piclist.com#nomail Going offline? Don't AutoReply us! >> email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > -- FCC Rules Online at http://www.hallikainen.com -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu --------------------------------- Do you Yahoo!? Friends. Fun. Try the all-new Yahoo! Messenger -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu