# Modbus RTU (RS-485 Cable-USB) **URL:** \ **Category:** Ignition\ **Tags:** ignition80\ **Created:** [April 8, 2022, 11:39pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-rs-485-cable-usb/58245 "2022-04-08T23:39:42Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Reyes](https://avatars.discourse-cdn.com/v4/letter/r/ccd318/32.png) [@Reyes](https://forum.inductiveautomation.com/u/Reyes)\ **Post date:** [April 8, 2022, 11:39pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-rs-485-cable-usb/58245/1 "2022-04-08T23:39:42Z")
We have many computers with the SCADA installed (clients) around the plant. I have the Gateway Serial Support Module and the Modbus Driver module. I’m trying to install a device that uses Modbus RTU RS-485-USB Cable. The procedure is: -Create a new device connection. - Modbus RTU. NEXT -Assign a name and description. -Assign a Serial Port (COM). Here is my question. Can I connect my device to one of the PC ports (in the network) and assign that COM number and will it work? In the videos, they said to assign a PORT but I think should be a COM port of the Server computer not of any computer right? (And our server is remote). ---
**Author:** ![josborn](https://avatars.discourse-cdn.com/v4/letter/j/4bbf92/32.png) [@josborn](https://forum.inductiveautomation.com/u/josborn)\ **Post date:** [April 9, 2022, 12:02am UTC](https://forum.inductiveautomation.com/t/modbus-rtu-rs-485-cable-usb/58245/2 "2022-04-09T00:02:37Z")
That won’t work, it would need to be connected to the gateway. This may be an application for a device like this: [https://www.digi.com/products/networking/infrastructure-management/usb-connectivity/usb-over-ip/anywhereusb](https://www.digi.com/products/networking/infrastructure-management/usb-connectivity/usb-over-ip/anywhereusb) ---
**Author:** ![yifeiliu08](https://avatars.discourse-cdn.com/v4/letter/y/bbe5ce/32.png) [@yifeiliu08](https://forum.inductiveautomation.com/u/yifeiliu08)\ **Post date:** [April 9, 2022, 6:33am UTC](https://forum.inductiveautomation.com/t/modbus-rtu-rs-485-cable-usb/58245/3 "2022-04-09T06:33:14Z")
I also have many 485 device need transfer the data to ignition but I don’t use the Serial Support Module, here is my structure 1. Use 1 siemens 1200 PLC write the PLC software to read the data from the 485 device 2. Ignition can use opc-ua connect to that simenes PLC ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/9/5/95f20e44b58e6e5ff5431e0de82ec019b7003209.png) ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [April 9, 2022, 2:05pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-rs-485-cable-usb/58245/4 "2022-04-09T14:05:19Z")
I’m going to bet a Moxa NPort 5130 (RS-485 via Ethernet) is cheaper than a Siemens 1200, and requires no external programming software. The IA Modbus driver offers RTU over TCP without needing the serial support module. (As does my own [Advanced Modbus driver module](https://inductiveautomation.com/moduleshowcase/module/automation-professionals-llc-advanced-modbus).) ---
**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\ **Post date:** [April 9, 2022, 2:06pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-rs-485-cable-usb/58245/5 "2022-04-09T14:06:28Z")
> [@pturmel](#): > > The IA Modbus driver offers RTU over TCP without needing the serial support module. It does, but I always recommend not using it, because RTU over TCP is conceptually flawed. Just spend the few extra dollars for the Moxa that will actually convert to Modbus TCP. ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [April 9, 2022, 2:37pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-rs-485-cable-usb/58245/6 "2022-04-09T14:37:17Z")
> [@Kevin.Herron](#): > > because RTU over TCP is conceptually flawed I strongly disagree. You just need to configure the intermediate device to buffer correctly, as described in my module's user manual. A Moxa is far more reliable at such timing than any PC's serial port. { Not to knock the Modbus TCP gateway product.. that's nice too. } ---
**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\ **Post date:** [April 9, 2022, 2:43pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-rs-485-cable-usb/58245/7 "2022-04-09T14:43:33Z")
Meh, that you need a special application note I think favors my assertion. Modbus ASCII over TCP, or Modbus RTU over UDP, make far more sense. Unfortunately they are pretty rare. ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [April 9, 2022, 2:50pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-rs-485-cable-usb/58245/8 "2022-04-09T14:50:32Z")
Meh. Ethernet to Serial converters pretty much always need some configuration, like port parameters, so noting the one other parameter to set for correct operation is not a stretch for a user. (That setting makes IA’s module behave, too.)