Computer Interfacing
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802.3af standard defines power over Ethernet

Small devices can be powered directly via the ethernet cable


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Joined: 13 Mar 2007
Posts: 145
Location: Netherlands and Kazakhstan

Mar 27, 2007 6:51 pm

Using the RS232 port to supply power for small devices is a common application. All serial mouses for example use the data and handshaking and lines to provide the power needed to operate the device.

Using the RS232 port as a power supply is not officially supported by the standard and success depends on many factors like the driving power of the driver ICs. To overcome this problem USB has a built in power source. For other small devices like small ethernet switches it would be nice if they could also draw their power from the data lines, but unfortunately until now this wasn't possible. The 802.3af standard defines a way of power distribution over an ethernet network. An interesting article about Power over Ethernet, or PoE for short, can be found at

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