Newsgroups: comp.dcom.lans.ethernet
Subject: Re: Can a standard NIC be triggered to send an electrical signal?
References: 
[email protected] (NANewbie) writes:

> Hi!
> 
> Does anyone know if a standard NIC can be configured to send an electrical
> signal down a cable? If yes, then can we write a program that can do that?
> How? Thanks.

To my knowledge there is no standard configuration / feature for NICs 
to send any single pulses to the line when commanded. 

With a normal 10Base-T Ethernet card normally when nothing 
is transmitted, the line is silent (only some link pulses 
could sent every now and then). When you transmit a packet, 
the Ethernet card sends a series of bits to the line 
presenting the data of the data packet. 

So with such card you just need to send a packet, and the 
card sends a set of electrical signal pulses to the line...
Any packet will do. 
With a TCP/IP networking send out ARP or UDP packet.

With 100 Mbit/s Ethernet (100Base-TX) things are not that simple..
When Ethernet card is transmitting data, you get bits on the line. 
But even when the card is not transmitting any actual data, there 
are bits traveling through the wire (a known bit pattern that 
keeps the data clocks on the oppostite ends of the link syncronized). 

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/