http://elecraft.85.s1.nabble.com/Pull-up-Question-tp2441352p2444957.html
> 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
Thank you for the clarification. The pull-ups were not visible on
the schematic.
> power the pullups.
port or the Yaesu "band data" jack. Yaesu in particular sources
+13V on those lines (and the "inhibit" line from the Quadra).
... Joe, W4TV
> -----Original Message-----
> From: Jack Brindle [mailto:
[hidden email]]
> Sent: Sunday, March 08, 2009 12:36 AM
> To:
[hidden email]
> Cc:
[hidden email]; '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:
[hidden email]
> >> [mailto:
[hidden email]] 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
> >>>
> >>>
> >> ______________________________________________________________
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