That is the answer I was looking for. We have these multi-poe boards we designed and had a bunch manufactured ... just passive devices that take an input voltage and spread it across 9 ethernet ports with two of the ports switchable between the input voltage and 12V. The signal side of the ethernet ports go to mirrored ports on the other side of the board to plug into a switch/router. I was thinking that if there was an easy way to sense the connection, I could throw in an XOR chip and a few small relays to make a cheap remote power cycle per port by simply disabling the port on the switch or router on the signal side of the board. Since the switch chip is involved, it becomes a much more complex and expensive part.
Cameron On 3/11/2010 2:38 PM, Lawrence E. Bakst wrote: > The link LED and all other LEDs for Ethernet Jacks/Connections are driven by > the Ethernet PHY chip or the Ethernet chip itself the PHY is integrated. > > Link is turned on by the PHY sensing the LIT (link integrity test) in 10BaseT > which I believe has become part of the auto-negotiation protocol in later > standards. This is part of the Layer-1 (Physical Later) protocol in the spec. > http://en.wikipedia.org/wiki/Autonegotiation > > So to be clear it's not just a LED hooked up to one of the wire via a > resister or some analog hack like that. The PHY knows that their is another > PHY on the other side of the cable and if the PHY sees the other PHY it turns > on the LINK light. PHYs often provide other lines to show collision, speed, > and duplex and these can be tied into other individual LEDS or bi-color LEDs. > > If the link lights are on at both ends the connection is good. It still might > be the case that a duplex mismatch or bad auto-speed negotiation could cause > problems. Both of these problems show up from time to time, especially on > older gear. For both cases the cure is often to fix the speed or duplex on > one side and that prevents the auto-negotiation from failing. > > One cause of not getting a link light is that a MDI/MDI-X mismatch. Most > newer chips have auto MDI/MDI-X which prevents the problem in most cases. > > leb > > At 12:52 PM -0500 3/11/10, Robert West wrote: > >> Yeah, but which circuit? The transmit, receive or maybe the unused pairs? >> >> That got me wondering also. >> >> Anyone know what pair triggers the light??? >> >> Bob- >> >> >> -----Original Message----- >> From: wireless-boun...@wispa.org [mailto:wireless-boun...@wispa.org] On >> Behalf Of Justin Wilson >> Sent: Thursday, March 11, 2010 12:15 PM >> To: WISPA General List >> Subject: Re: [WISPA] Ethernet LEDs >> >> Simple terms it's the completion of a circuit. >> >> --- >> Justin Wilson<j...@mtin.net> >> >> On Mar 11, 2010, at 11:29 AM, Cameron Crum<cc...@dot11net.com> wrote: >> >> >>> This may be a little out there, but does anyone know what causes the >>> "link" light to show on an ethernet jack when the cable is plugged in? >>> Is it as simple as just attaching an led to one of the signal wires, >>> or >>> is there some logic in there. Just curious. >>> >>> >>> --- >>> --- >>> --- >>> --- >>> -------------------------------------------------------------------- >>> WISPA Wants You! Join today! >>> http://signup.wispa.org/ >>> --- >>> --- >>> --- >>> --- >>> -------------------------------------------------------------------- >>> >>> WISPA Wireless List: wireless@wispa.org >>> >>> Subscribe/Unsubscribe: >>> http://lists.wispa.org/mailman/listinfo/wireless >>> >>> Archives: http://lists.wispa.org/pipermail/wireless/ >>> >> >> ---------------------------------------------------------------------------- >> ---- >> WISPA Wants You! Join today! >> http://signup.wispa.org/ >> ---------------------------------------------------------------------------- >> ---- >> >> WISPA Wireless List: wireless@wispa.org >> >> Subscribe/Unsubscribe: >> http://lists.wispa.org/mailman/listinfo/wireless >> >> Archives: http://lists.wispa.org/pipermail/wireless/ >> >> >> >> -------------------------------------------------------------------------------- >> WISPA Wants You! Join today! >> http://signup.wispa.org/ >> -------------------------------------------------------------------------------- >> >> WISPA Wireless List: wireless@wispa.org >> >> Subscribe/Unsubscribe: >> http://lists.wispa.org/mailman/listinfo/wireless >> >> Archives: http://lists.wispa.org/pipermail/wireless/ >> > > -------------------------------------------------------------------------------- WISPA Wants You! Join today! http://signup.wispa.org/ -------------------------------------------------------------------------------- WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
