HMI and Message Display Screen On PLC

I was trying to connect an HMI and a LED MEssage Display Screen to my PLC. My PLC has two serial port supporting Modbus. Unfortunately one of the serial port can act as a slave only. SO my question is, can I connect the LED message Display screen to the slave only serial port. I think we can only send the message to the LED screen only if the PLC is master. All three components support the Modbus protocol. Or can I connect my LED display to My HMI?

Any help would be Highly appreciated. Thank you.

Give us part numbers, makes and models.

General info:
A Modbus RTU slave cannot initiate messages, so I would think that the HMI may still be able to work with it and act as the Modbus RTU master. Use the PLC serial port that can be the Modbus master to control the LED display.

Welcome to the forum!

Thank you for your prompt Reply. The PLC i have is Directlogic5 . My LED Message board is Viewmarq1 and my HMI is EA3-T4CL

I did it before with a DL05 and a display, should be fine... I did end up getting a ecom for the DL05 so I could connect also and then ended up putting everything on the Ethernet

This is the manual for the COMs https://cdn.automationdirect.com/static/manuals/d0user/ch4.pdf

Here are all the user manuals
https://cdn.automationdirect.com/static/manuals/d0user/d0user.html

And yes your PLC is the master the display is a slave, the HMI will need to be on the other port

Do you have all the parts yet? if not you may want to consider Ethernet

Thank you so Much @geniusintraining. I don't have the parts yet so I am considering ethernet as you suggested. One more question. In the HMI-PLC communication, WHich one acts as the master?
Thank you.

I think they would both be masters, I think... but not positive, my DL05 project was over 10 years ago

This is the ecom https://www.automationdirect.com/ad...plc)/communications_-a-_networking/h0-ecom100

You may want to consider a PLC that has the Ethernet built in... AD has several

I just started using these and they seem like a nice product
https://www.automationdirect.com/ad...ctivity1000_(stackable_micro_plc)/cpus/p1-540

I know the Clicks also have Ethernets available and both should be cheaper then the DL05

Here are the Ethernet Clicks I use https://www.automationdirect.com/ad...(stackable_micro_brick)/plc_units/c0-10dd2e-d

You may want to give AD a call and see if they have any suggestions that may be a easy setup with all 3 pcs...

Good luck on your project

Okay. Thank you so much.

I would use the HMI as a Master, the PLC and Led dispaly as slaves over RS485 modbus RTU

With Modbus RTU, you can only have one master, and the HMI needs to be a master in order to communicate with the PLC without a whole bunch of extra logic in the PLC.

If you have not bought hardware yet, by all means use a Click with Ethernet. Modbus TCP allows for more than one client and more than one server so things will be much MUCH simpler for the integrator, not to mention the ability to talk to both devices simultaneously from a PC with the simple addition of an Ethernet switch.

The Click software takes a lot of the headaches away that you have with DirectSoft when dealing with data formats especially. The software is free and relatively trouble free.

Generally, HMI panels like the C-More, PanelView, Maple, etc are the communications masters. Based on which screen is currently displayed to the operator, they request whatever data they need to refresh the screen as frequently as possible. Data displayed on a screen that isn't visible doesn't need to be refreshed unless that data is defined as an alarm condition.
The OP's Viewmarq display is a Modbus slave (page 2 of the linked manual).
The DL05 has two serial ports, so one could be set up as a Modbus master, the other as a slave. Doing so would mean that either the HMI or the Viewmarq display would have to be disconnected in order to connect with Direct Logic software to make program changes. That's why Genius in Training suggested adding the ECOM module in the DL05's single expansion slot.