[Elecraft] K3 Firmware updating

[Don Wilhelm]

Larry,

RS-232 cables cannot be simply daisy-chained or Y'ed.
Like normal logic lines, there can be only one driver on any one signal 
line.   Some logic families do allow 'wire-or' and 'wire-and' 
connections with the proper selection of drivers, but that is a special 
case.
The receivers are high impedance, and one can have several receivers on 
the cable (that is what the SteppIR Y cables do - they only listen to 
the communications on the line)

The drivers are the problem - along with the switching levels.  The 
levels must be maintained either below -3 volts or above +3 volts so the 
receivers will not be detecting invalid data levels.  If two drivers are 
on a signal line, and one is trying to provide an ON level while the 
other is trying to provide an OFF level, confusion will reign.  Even if 
one driver is powered off, it can still draw current from the line which 
will interfere with the other driver.  The RS-232 drivers are not like 
tri-state devices which effectively disconnect from the line when 
powered off.

So as a result, RS-232 is a point to point system only, and except for 
special circumstances, that restriction must be followed.

73,
Don W3FPR

Larry - K2GN wrote:
> Joe:
> Are you saying the there is a power requirement for the microHAM even when
> it is turned off????
> Or do you mean the RS232 control lines? If so, and the device gets powered
> down, doesn't it's hold on the control lines go away???
> de K2GN - Larry - http://k2gn.com
> K3 S/N - 3278    P3 S/N - ????  (Ordered)
>
>
>
>   
>> Can I put a "Y" adaptor on the RS232 and run a USB to my laptop, and 
>>     
>  > leave the microHAM powered off? 
>
>   
>