Micrologix 1400 and Modbus RTU

[mikeexplorer]

I have a spare Micrologix 1400 Series B I bought used on Ebay awhile back. I had thought of it as a spare PLC for my train project but I screwed up on the model number as it does not have the analog I/O built in. I tested it and everything works on it.


I saw a thread about Modbus communication and I may be doing a project in the future at work where I will need to use Modbus but I don't have any experience with it. I bought a cheap relay board to start learning.


My question is, Is it possible to use the DB8 serial port (comm port 2) for Modbus? I want to reserve the round port (comm 0) for an HMI panel which I have a used spare. The panel does not have ethernet (Its an automationdirect EA9) I saw on one website where it said I could use Com 2 but I have to make my own cable. I can't find a diagram for this cable.



Mike

 

[OkiePC]

CH2 (9 pin D Male) is RS232 only but the port configuration does support Modbus.

CH0 (round connector) supports Modbus RTU and has both RS232 and RS485 pins so you can use either if you make the right selection and use a cable that exposes the right pins. My preference for RS485 is to buy a 1762-NC01 breakout board like this:

https://www.plccable.com/allen-brad...485-cable-8-pin-mini-din-to-6-pin-micrologix/

It has clearer markings than the brand name at half the price.

I am not sure if all the correct pins are populated in a regular 1763-CBL-PM02 cable that you allow you to make your own RS485 cable.

In any case, to use CH0 with RS485 you have to choose the option on the port config dialog box dropdown list that specifies '485-No Handshaking'

 

[jaden]

For information on the Automation Direct EA9 cable, AD's website has cable info . Look for the manual (PLC Comm) on the support pages.

 

[Ken Moore]

Many years ago, I worked at a place that got a great deal on a new 1200 ton chiller. It was a cancelled order, so we had no influence over it's controls. It came with a BACNET controller, that also supported Modbus RTU. I purchased a ML1400 and pulled the data from the chiller, and fixed all the implied decimals, store to reals, and used the built in ethernet connection to connect to our OSI-PI historian. Management was pleased.

Using the ML1400 as a Modbus master was very easy, IMHO.

I have also configured vendor supplied ML1400's to act as Modbus slaves, they were connected to a Siemens PCS7 DCS via Modbus TCP. The ethernet port on the ML1400 can support two protocols at the same time, but not three. If you use it as slave to a traditional Siemens S7-300 or 400, you need to swap the byte order when writing your data to modbus bits, but not with integers.

 

[mikeexplorer]

For information on the Automation Direct EA9 cable, AD's website has cable info . Look for the manual (PLC Comm) on the support pages.

I did download the manual for the EA9 panel and I did see the DB9 to DB15 cable, but it said SLC type PLC, but when I read it again, it also does state Micrologix. (I missed that part)



I checked with RSLogix, I can configure COM 2 to be DF1 so that would be compatible with the EA9 Panel. So that will work for me.
Use COm0 for Modbus , Ethernet to program, and COM2 for the HMI


I have the parts needed to build my own cable for the HMI, Ill just purchase the modbus cable mentioned two posts above.



Mike