Natale,
A "pull-up" resistor is normally located at the end of the signal path
that contains the receiver (in the case of the TX INH, the K3 end is the
driver for the circuit).
The resistor "raises" the level on the line - rather than just allowing
the line to float to any voltage.
When the driver is not conducting, the pull-up resistor assures that the
voltage level at the receiver will be close to 5 volts, and then when
the driver conducts, the voltage at the receiver end will go close to zero.
The function is the same as a collector resistor in a normal transistor
driver. For digital logic, when the signal is sent over a line between
two units, it is common to put that resistor at the furtherest receiver
location rather than at the driver - that reduces noise pickup on the
line - not normally a problem for short lines, but always a possibility
with longer runs, or on lines with multiple receivers.
The voltage is supplied by the receiver at the far end of the line. and
must conform to the requirements of the driver in the K3 (not usually a
problem with 5 volt logic).
In the case of the shared functions for that K3 ACC pin, it would not
work properly in some cases if the resistor were located in the K3.
"Receiver" in this context is not a radio receiver, but a digital logic
circuit.
73,
Don W3FPR
On 6/2/2011 2:49 PM, Natale Borghetti wrote:
> Hi OM,
>
> I need some help...I have to connect my K3 to Station Master to have the TX INIHIBIT, I have understand that have the TX INIHIBIT at pin 7 of K3 and this has to be connected to the TX INIHIBIT of Station Master.
> I read page 19 of K3 Manual that says:
> "An external 2.2 to 10 K pull-up resistor (to 5VDC) is required".
>
> Well that is NOT very clear to me.....(perhaps I am to old...Hi), could some more clever explain better how to do it or a small schematic will be appreciated as example where is the 5VDC ???
>
>
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