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
