Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I got a serial to ethernet device connected to a Serial (COM) port on a Linux machine (debian etch), I connected it correctly but it did not power up, I suppose I need to power the device port, anyone knows how to power it under linux?

Thankyou in advance.


Unfeasible with my requirements, Answer accepted and explanation in comments.

share|improve this question
up vote 1 down vote accepted

You dont. Well, waht device?

Serial ports do NOT (!) have power supply. Point. most devices - except thing like a mouse which may be able to sniff enough power using a circuit like - have a separate power supply.


  • For mice, it would be broken.
  • For a real device, connect the power supply and power on the device using other means (i.e. you can not start it using the COM port).

What device are you talking about?

share|improve this answer
A barcode scanner that has just one plug, from a Serial port to an ethernet port on itself. – Lex Mar 17 '10 at 8:32
Any weblink? I mean, serial to ethernet already sounds funny. ETHERNET has power over ethernet available. IF the thernet side provides it. Could be that device requires a POE ethernet port? What cable do you use to connect serial to ethernet? – TomTom Mar 17 '10 at 8:38 The cable is supplied by vendor, one end is a plug for a Serial port and the other a plug for the ethernet on the device. – Lex Mar 17 '10 at 8:44
Looks like not so easy... This one item made me wonder: Cable, RS-232, 25P, Female, Coiled, CAB-363 (Power available on pin 9 of the connector or through external power supply) You definitely do NOT power that through a STANDARD com port - read the documentaiton, contact users. Somewhere this device needs (more) power and you may have the wrong cable etc. It is definitely NOT drawing power from a normal COM port. The documentation should tell different ways to pwoer it. – TomTom Mar 17 '10 at 9:10
That device has nothing to do with ethernet, Lex. Lots of devices use RJ-45 connectors (which are a separate thing from ethernet) for plain old serial, which is what that is. There are also references to power cables on that page. I'll bet you need one of those, plus software compatible with the scanner. – Nicholas Knight Mar 17 '10 at 9:13

There are mobile data collection computers that have standard pin out that supplies power on one pin to external devices like bar code scanner guns. The port power is controlled by an application that manufacturer of the mobile computer built or uses.

Pin Number  Signal Name     I/O to Computer Description
1     DCD               I             RS-232 Data carrier detect
2     RXD               I             RS-232 Receive data
3     TXD               O             RS-232 Transmit data
4     DTR               O             RS-232 Data terminal ready
5     GND              PWR            Signal Ground
6     DSR               I             RS-232 Data set ready
7     RTS               O             RS-232 Request to send
8     CTS               I             RS-232 Clear to send
9     PWR_OUT              PWR            5VDC 0.5A to power external devices
DB9 Shell     C-GND            PWR            Chassis Ground
share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.