I am working a project where I want to connect and control, using Labview,

  • TDK-Lambda Power Supply
  • Process Vacuum Controller Ion Gauge (MODBUS interface)

They both have rs232/rs485 capabilities, just depends on a switch on the back of the terminal and both connections are with a rj45 jack (I will attach relevant manual). And connect via a RJ45 cable, and I want to connect it to a computer.

Now, I've set up a .vi that should be able to connect to, or at least discover, the devices but to no avail. It might be because I am using a regular Cat5E Patch/Ethernet Cable and it therefore not the right pinout. I've tried to read some post and/or white papers about the subject, but these devices are specific and have different pinouts.

So my question is, how to I go about using an rj45 cable for serial communications? Can I simply connecting a cat5 cable to my laptops ethernet port and to one of the devices serial rj45 jack? Or am I missing something major?

This is my first attempt at anything like this, but I have used Labview to connect to serial DB9 to usb adapters and able to communicate.

Here is a link to the PVC Ion Gauge Manual And the TDK-Lambda Power Supply

I know I am asking for a lot of help here, but I am super lost and any help is much appreciated.

  • 3
    \$\begingroup\$ Serial over RJ45 is not Ethernet. You will probably have to look up the wiring of your peripheral's specific pinout and construct a custom adapter cable to a USB-serial adapter. \$\endgroup\$ Commented May 20, 2015 at 15:54

1 Answer 1


You are missing something major. You CANNOT connect a serial connection to an ethernet port and get anything useful out of it.

You will need an adapter from RJ45 to an RS232 conector (usually Sub D9) or to an RS485 connector (Not sure what this looks like.) You will then need the appropriate interface on your PC - that would be a serial port for the RS232, or a special interface for the RS485. Both of these can be had as external units that connect to your PC via USB.

You will then need a VI for Labview that can use the adapter. RS232 should be standard, I don't know about RS485. You can probably purchase an adapter from National that will include the correct VI and or drivers.

Both manuals include information on how to wire the RJ45 to a serial cable. You will have to either build them yourself or try to order them from the equipment manufacturer.

  • \$\begingroup\$ Ah okay, that's pretty major. But I can make the cables the manual outlines. I'm just wondering, do you know any schematics I can use to make my own conversion hub? Instead of making individual cables with db9 connections, I could just funnel them into the hub and only have one output to connect to the computer \$\endgroup\$
    – Shahab
    Commented May 20, 2015 at 16:52
  • \$\begingroup\$ It isn't that easy. The converter that attaches to your PC has a fair amount of smarts. On the one side it talks to your PC over the USB bus, and on the other side it takes in data from the serial bus. In the middle it has to convert it from protocol to another - and that in both directions. You would also have to scratch up a driver for windows and something for Labview. Better to go with commercial stuff. \$\endgroup\$
    – JRE
    Commented May 20, 2015 at 17:27

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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