ML1500 and modbus

Ron Brown · Nov 22, 2005

I am working on a project with a ML1500 LRP using MODBUS protocol communications.

I have most of this working but need to set up some "text" messages to be displayed at different points in the logic if certain conditions or true. I have yet to find out how to load these messages in the PLC though.

Some examples that I have are from a DL06 automation direct plc but they handle this alot different from what I can tell so for.

Has anyone done this before with this plc and if so what is the best way to do this?

Thanks,
Ron Brown

rsdoran · Nov 22, 2005

You did not state HOW you would display the messages, most HMI's can have preconfigured messages that are triggered by a bit in ladder logic. In most cases the page with the message can/will appear if triggered.

jstolaruk · Nov 22, 2005

If you want the ASCII text to be in a binary or integer file (example B3 or N7), the easiest way to enter the text is to call up the data table viewer window and place the radix in ASCII mode. That will allow you to directly type in the text in to the data file. Each integer location will contain two ASCII characters. Just go to the first address and start typin in the text and the window will store it accordingly.

The other way is to create a new data file of type string though I'm not sure if the HMI can read that data type via Modbus.

Ron Brown · Nov 22, 2005

The message has to be setup in the plc and loaded to a preset memory location that the HMI will monitor for any new messages.

The plc will also have to clear this message out after the HMI gets the message which I think I understand how to do this once the message is placed.

jstolaruk · Nov 22, 2005

Ron Brown said:
The message has to be setup in the plc and loaded to a preset memory location that the HMI will monitor for any new messages.

The plc will also have to clear this message out after the HMI gets the message which I think I understand how to do this once the message is placed.

You can execute a COP instruction when you want the copy to occur from some other storage location. FLL will clear or place any character you wish into that memory location(s).

Ron Brown · Nov 22, 2005

Thanks for the input. I will try that out and see what I get. Modbus will not read for that data file though, but I can I load the information in there and do a COP to move that info into the memory location that I need?

jstolaruk · Nov 22, 2005

Example: The primary memory location you are monitoring for a message is N7:0-N7:9, a 20 character message.

Storage could be at n11:0-N11:9. When you need to, execute a COP #N11:0 #N7:0 10. That will copy the message that you stored in N11:0 to the memory location N7:0 that is being monitored.

I hope that helps.

Ron Brown · Nov 22, 2005

What would be the best method for developing the messages to start with? I realize I can go to the file itself and start typing the information, but would be better to load these through the logic on power up instead and what would be the best method for loading these?

Sorry for all these questions but this is the first time I tried doing this in the many years I have been programming this type of controller.

jstolaruk · Nov 22, 2005

As long as the battery is good, placing the messages in data table memory is as good as the PLC program in memory. If the program is backed up to EEPROM, I'm pretty certian the data tables are too. Using logic to initiate messages in the data tables would be pretty cumbersome.

Ron Brown · Nov 23, 2005

Okay I tried this and am getting the message loading into the holding register. The problem I have having now is the HMI looks for one of the function coils to be turned on. The function coil is just one of the modbus coils and it appears to be set up correctly but it is not working.

I am using the COP instruction to move the #N7:0 to the #N13:70 holding location for the message.

I am using the B10:10 - B10:12 for the above mentioned function coils.

I am using manually entering the message in the N7 register for now to try and get this working.

If anyone has any suggestions that would be great.

Lancie1 · Nov 23, 2005

I can only guess (remote troubleshooting is somewhat of a **** shoot), but check to see that the coil you think is actually turning on. Also, check to see if it needs to be on continuously to display the message, or just a on/off momentary pulse. Many HMI displays, that I am familar with, have a "handshaking" routine, where the PLC turns on a bit, then the HMI reads that bit and either turns it off again, or turns on a different bit, to tell the PLC "message received".

jstolaruk · Nov 23, 2005

What HMI are you using?

ML1500 and modbus

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