I’m trying to setup a couple of tags in an AB Micro850 PLC referencing this thread. However I’m lost on the setup. I’ve never used Modbus before. Below is a snapshot of the plc program, I want to start off with a tag to show if the machine is on or off which I think reading set coil _B001 is what I want?? I tried addressing it in ignition tag as [WoodChipper]C000001, but nothing.
Yes, you have to map each variable you want to access via Modbus.
I’ll give it a shot after machine shut down
I was able to map the variables and upload it to the PLC. It worked well, I thought this was going to be more complicated but was actually pretty simple. thanks
I am able to connect to a Micro850 using the Modbus TCP protocol but I can’t get values from it. I have the Modbus Mapping setup in the PLC as shown here:
I have tried many different names in the OPC Item Path. Note: The tag names in pic below match the name used in the OPC Item Path, so you can see I’ve tried many names in desperation. I would think HR1 would work though.
I don’t know how to determine if this problem is on the PLC side or Ignition side. Can anyone suggest how to determine the cause of my problem? Oh, please ignore that the Tag Browser is showing “Connecting” when I took the screen print, we turned the PLC off at the time but Ignition does show Connected when the PLC is on.
Did you enable ModbusTCP in CCW? (As per the little warning top right of your first image)
Use ModPoll or similar software to rule out Ignition as a start
Yes, Modbus TCP was enabled or Ignition wouldn’t be able to connect to it. ModPoll was helpful. I found that having a single invalid tag pointing to a Modbus address in Ignition was causing my good tags from getting data from other Modbus addresses. Once I disabled all my tags where I was using trial and error, I enable a single tag and it worked.
I encountered an issue similar to this today. I was able to access some Modbus registers in the Micro850, but when I started trying to access additional Modbus registers all my existing working tag values went to Bad.
The problem was that the registers in the Micro850 were not in a continuous block and if you request a Modbus register from the Micro850 that is not configured, it will return an Error. By default the Ignition Modbus driver has Span Gaps turned on, which was causing Ignition to request registers that were not in the Micro850, to which the Micro850 return Error and then all my previously working tag values went to Bad. Once I realized what was going on, I disabled Span Gaps and all the tag values started working correctly.
Thank you for this update!
Has anyone had no errors connecting, values appear in the tag browser, but the values for the float be incorrect? First time trying to get modbus communicating. I probably am misunderstanding the radix and modbus address during the setup on the gateway... I did have to start the modbus address
at 2 instead of 1 or else all the values bounce around.
Some combination of setting zero-based addressing and/or swap words should work for you (in the device advanced settings on the Ignition side).
FWIW, if you do much with this family of processors, you might want to look at my latest EtherNet/IP driver. (So you don't have to set up Modbus in the ML8xx.)
