I am trying to connect two devices to Ignition in the following manner. Device1 and Device2 are daisy-chained on the same RS-485 network. This RS4-85 cable comes back to a MOXA N5232i Serial to Ethernet converter and is connected to our network switch via a Cat5 Ethernet cable. I have double checked the wires on the RS-485 network, the IP address of the MOXA I am communicating with and the Slave Addresses of Device1 and Device2. I am using the Modbus RTU over TCP module to connect to these devices in the gateway and I have created a UDT with corresponding tags for these devices in Designer. I don't know why but the Designer seems to read only one of these devices at a time and the other one shows a red connection. "View Tag Diagnostics" simply says "Bad Not connected, Value should be received from another variable" and then randomly reads the right value and then goes right back to red. I have used these MOXAs with other devices in my facility over the same configuration and it works just fine. The cables have been checked twice as well for any damage or otherwise and appear to be perfectly fine.
Any help diagnosing this issue would be fantastic.
If they are on the same physical circuit, then they are required to have distinct slave unit IDs, and you must use a single Ignition device definition to talk to them. There can be only one master on an RS-485 channel.
Yes, sorry I didn't make that clear. Both these devices are on the same physical circuit but my Ignition server is only communicating with the MOXA. There are separate slave unit IDs for both devices
Right, but you can only make one Ignition device for the whole channel. Then use the separate unit IDs within the single Ignition device. Did you do that? (There can be only one connection from Ignition to the TCP+RTU port on the Moxa.)
I made that change as described on the device in the ignition gateway. Now the values for either tag do not update, just flash between red and black in the designer. Nothing in the reference log for either tag.
Did you find a solution? I’m having the same issue. Two identical devices on the same RTU network one master, ID are set to 1 and 2 in ignition, and devices themselves are set to drop numbers 1 and 2 for the network. If I delete one or the other from designer, value (coms) work fine, but if both are setup in designer, value’s flip black from (good) to red (bad). Baud rate 19200 8N1. estimate 900 tags on each device.
Modbus RTU is a single-master protocol. If you make two devices in Ignition to scan different drops on the chain, the masters will interfere. You have to use a single device in Ignition and use the unit prefixes in the OPC Item Paths to distinguish the drops.
Other notes:
The spec for RTU requires either parity or two stop bits, for a character frame 11 bits long.
19200 baud will transfer <860 16-bit registers per second, presuming all are packed together in memory (no gaps, all requests get 125 words).
