>You could send a square wave out of the pic at different freqs
>to identify each cable or you could simply attach every wire to
>the pic at one end and a pic on the other end and write a program
>that will step thru all of the cables by simply using a dc voltage
>to match up each line using some type of algorithm and an lcd display.

My thought too. use the PWM module to generate a suitable frequency, and
apply this to the enable input of a 74HC138 or similar decoder (depending on
how many lines you want to do at a time you may need more than one). Each
output then drives a separate circuit, and the inputs come from the PIC to
select which line is under test.

>Once a match is detected, you can repeat the process. But how do
>you notify the other Pic to move to the next cable?

Two possibilities I see. One is the detecting PIC loads the sensed line with
a short, and the sending PIC detects the drop in output level from the
short, removes drive and waits for a moment. The other possibility, and
probably the better one, is for the detecting unit to short the line with
drive from its own PWM module, but at a different frequency to the sending
one. The sending one then detects this tone and knows the line has been
detected. In either case once the line is detected the sending unit then
sends a different tone to signify that it is moving to the next line, at
which point the detection end terminates the "detected" signal, and goes
back to search mode.

Using this method various tones could be used to signify crosstalk detected,
short between lines detected, and also the possibility of using frequency
shift keying to send a message to the other end (e.g. telling the operator
what to label the line) which could show on an LCD display. Alternatively
the UART could be brought out to a connector for connection to a laptop for
use as a terminal if an LCD screen and keyboard were not in the costings.

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