Navtel 9460 Protocol Analyzer info?

Dave Dunfield dave04a at
Tue Apr 12 22:12:33 CDT 2005

>> On 4/12/05, Vintage Computer Festival <vcf at> wrote:
>> > I can't remember what the software I used was called, but I think I still
>> > have it somewhere and  can check.  It came with a special double-headed
>> > cable though, and unless that cable was just a simple Y-split, I don't
>> > know if making one from scratch would be feasible.
>> The physical cable used with HP line analysers is a simple Y-split -
>> 25-position ribbon cable, two DB25F and one DB25M (or the other way
>> round... can't quite remember).  You can wedge the cable between two
>> devices, then attach the free end to the HP pod (or just plug a DB25
>> cable right from one unit direct to the pod if you are using the HP to
>> originate or consume bits)
>> What I'm not sure of is if the HP pod has anything special in the way
>> of drivers/receivers to keep from loading the line as it monitors
>> things.  I could open up a pod and see what's inside...
>I have limited experience with this as I only tried it once, but when I
>did I noticed that either one or the other computer was greedy and took
>all the bits for itself, and the other computer didn't get any signal, so
>I always assumed you needed some sort of "special" cable in order to split
>an RS-232 signal.

I have a couple of simple serial datascope packages in my Labtools ...
I don't supply cables, I just give details on how to make them.

Basically, there are two sets of signals to monitor, one going from
DTE -> DCE, and one going from DCE -> DTE ... What the "Y" cable does is
simply connect the DTE generated signals to the input signals on one COM
port, and the DCE generated signals to the input signals on the another
COM port. The software reads the two com ports and displays the two
signals paths in a standard dual/split line format, with DTE signals on
one line, and DCE signals on the other.

(Since PCs are DTE's, the input signals to the COM ports are the DCE
 lines at the PCs serial connector).

The DTE signals (outputs) from the PC COM ports are not connected, so the
PC does not drive either side ... it just passivly monitors the traffic
on the line.

For short runs at the speeds commonly handled by a PC serial port, the
extra loading of the passive receiver is usually not a problem. One
limitation of this approach is that the PC cannot interact with the
devices. Some stand-alone/higher-end scopes feature simulation, injection
and other features which require that they be able to transmit on the
line in specific circumstances these usually have their own set of line
drivers and receivers, and act as a simple repeater during passive

dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools:
com             Collector of vintage computing equipment:

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