The KRC2 has on-chip pullups that handle the task. They are enabled
KRC2 is in BCD input mode. Thus external pullups are NOT needed for
power the pullups. We spec
>
>> 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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