Jack, > The KRC2 has on-chip pullups that handle the task. They are enabled > whenever the KRC2 is in BCD input mode. Thus external pullups are > NOT needed for the KRC2.
Thank you for the clarification. The pull-ups were not visible on the schematic. > The inputs are resistor-protected in case the driving device does > power the pullups. As is the case when connecting the KRC2 to either a computer LPT port or the Yaesu "band data" jack. Yaesu in particular sources +13V on those lines (and the "inhibit" line from the Quadra). 73, ... Joe, W4TV > -----Original Message----- > From: Jack Brindle [mailto:jackbrin...@earthlink.net] > Sent: Sunday, March 08, 2009 12:36 AM > To: li...@subich.com > Cc: d...@w3fpr.com; 'elecraft' > Subject: Re: [Elecraft] [K3] Pull-up question > > > The KRC2 has on-chip pullups that handle the task. They are enabled > whenever the > KRC2 is in BCD input mode. Thus external pullups are NOT needed for > the KRC2. > > The inputs are resistor-protected in case the driving device does > power the pullups. We spec > those inputs only for the TTL voltage range. > > -Jack Brindle, W6FB > ============================================================== > ========= > > > On Mar 7, 2009, at 8:42 PM, Joe Subich, W4TV wrote: > > > > >> Unfortunately, much of the ham gear available uses bare, > open inputs > >> and depends on the driving device to provide the voltage > and levels > >> it needs at its inputs. > > > > Let's see ... that would apply to the KRC2 in the "parallel input > > mode" along with the W9XT BCD-10 and the Yaesu Quadra for > starters. On > > the other hand the TopTen Systems BD-Y, the original microHAM Band > > Decoder, the Yaesu FL-7000, and Tokyo High Power HL-1.5Kfx, have > > internal pull-up resistors. > > > > 73, > > > > ... Joe, W4TV > > > > > > > > > >> -----Original Message----- > >> From: elecraft-boun...@mailman.qth.net > >> [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Don Wilhelm > >> Sent: Saturday, March 07, 2009 2:56 PM > >> To: Roger > >> Cc: elecraft > >> Subject: Re: [Elecraft] [K3] Pull-up question > >> > >> > >> Roger, > >> > >> That is where the situation gets 'sticky'. It all depends on what > >> the circuits at the end away from the K3 have implemented. > You have > >> two pullup resistors on each line and 2 separate voltage sources. > >> > >> 1) If the voltage to the pullup resistors in the internal > device do > >> not match the voltage to the pullup resistors in the K3, > there will > >> be a continuous flow of current through both pullups on any one > >> line when the > >> drivers are at their open, non-conducting state). If the > >> voltages are > >> close to the same value, this may not cause a problem, but if > >> they are > >> quite different (say one is 12 volts and the other is 5 > volts), that > >> could create a big problem. > >> 2) The drivers in the K3 (when at the low level) must carry > >> the current > >> provided by both pullup resistors. Whether that is a > problem or not > >> depends on the value of the pullup resistors and the current > >> capability > >> of the drivers. > >> > >> In my view of a good design, open collector (or open > drain) drivers > >> are the only thing to use. The terminating device can > determine what > >> voltage is needed for reliable switching at its input and > that device > >> controls the high level by providing its own pullup resistors. > >> Secondly, the pullup values can be sized according to the > high level > >> input current required by that device and can control its > immunity to > >> noise by controlling its input conditions. All is under the > >> control of > >> the external device designer. Unfortunately, much of the ham gear > >> available uses bare, open inputs and depends on the > driving device to > >> provide the voltage and levels it needs at its inputs. > >> > >> 73, > >> Don W3FPR > >> > >> 73, > >> Don W3FPR > >> > >> Roger wrote: > >>> Mike Fatchett, > >>> OK, but what happens when you use > >> them with devices that already work without them,e.g. > Array Solutions > >> 6 Pack and early band decoders? > >>> Roger K8RS > >>> > >>> > >> ______________________________________________________________ > >> Elecraft mailing list > >> Home: http://mailman.qth.net/mailman/listinfo/elecraft > >> Help: http://mailman.qth.net/mmfaq.htm > >> Post: mailto:Elecraft@mailman.qth.net > >> > >> This list hosted by: http://www.qsl.net > >> Please help support this email list: http://www.qsl.net/donate.html > > > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:Elecraft@mailman.qth.net > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
