Micrologix 1400 to Panelview C600 via Modbus

I'm working with a Micrologix 1400 and a Panelview C600. I can get them working together fine over ethernet, but am having trouble getting the same functionality over Modbus. When I verify the project, all the tags show an error that the addresses, data types, or controller names are incorrect. I suspect the issue is with the definition of the coil, contact and registers on the PLC. I'm pretty new to Modbus, so let me know if there's something obvious I'm missing.

Hemlock said:

...I suspect the issue is with the definition of the coil, contact and registers on the PLC...

Click to expand...

Have you the channel in the ML1400 configured for Modbus RTU Slave?

Are the Data Files created for "Coils", "Contacts", "Inputs", "Holding"?

What Modbus addresses are you using in CCW?

An example would help.

Regards,
George

Why would you use Modbus RTU serial between these devices ?

The PanelView Component terminals can address the same MicroLogix registers over DF1 serial that they can over EtherNet/IP.

Unless this is for a protocol test project, I don't see a reason to do it.

As George mentioned, in general to configure a MicroLogix 1400 as a Modbus RTU Slave, you define a different Integer (N) data file for each Modbus memory type. The most common one is Holding Registers, often referred to as "4xxxx" memory.

I have set up the data files for coils, contacts, input and holding registers. The project already uses Modbus on another channel. I wasn't aware that the PLC could be configured as a master on one channel and a slave on another. I hope to be get back to this today and give that a try.

I hadn't really though about the "why" Ken?

Hemlock,

Now I realize you felt constraint, protocol-wise, to what was already setup on the other port...

Hemlock said:

I have set up the data files for coils, contacts, input and holding registers. The project already uses Modbus on another channel. I wasn't aware that the PLC could be configured as a master on one channel and a slave on another. I hope to be get back to this today and give that a try.

Click to expand...

The 3 ports on the ML1400 are independent. You can configure the serial channels 0 and 2 for the same or different protocols...

Communication Options
The MicroLogix 1400 controllers provide three communications ports:

Isolated combination RS-232/485 communication port (Channel 0)
Ethernet port (Channel 1)
Non-isolated RS-232 communication port (Channel 2)

The channel 0 and channel 2 ports on the MicroLogix 1400 can be connected to the following:

• operator interfaces, personal computers, etc. using DF1 Full Duplex point-to-point
• a DH-485 network
• a DF1 Radio Modem network
• a DF1 half-duplex network as an RTU Master or RTU Slave
• a Modbus network as an RTU Master or RTU Slave
• an ASCII network
• a DeviceNet network as a slave or peer using a DeviceNet Interface (catalog number 1761-NET-DNI)
• an Ethernet network using the Ethernet Interface module (catalog number 1761-NET-ENI, or 1761-NET-ENIW)
• a DNP3 network as a Slave

The ports do not have to be configured for the same protocol, but even when doing so, you cannot pass the data in one port and out the other directly. You have to go through programming logic, using message instructions, which access the Data Files. All protocols access the same data format within these Data Files.

If you need the Modbus data on the existing port to interact with the C600 connected to the new port, then similarly, you will need to use message instructions, but the protocols need not match at all. The ports are reading into and writing from Data File addresses. Each protocol can access the Data Files that may or may not be in use with the other port's communications.

Example:

Channel 2 Modbus Master reads in 10 Holding Registers from Modbus Slave to N100:0 to N100:9

Channel 0 DF1 writes 10 words to C600 from N100:0 to N100:9

The data in Integer file N100 is the same format for both channels, regardless of which protocol is used.

You should still be able to get this working using Modbus RTU Slave on the new port, if you so wish, but Modbus is a bit of a pain to address compared to DF1, if you have the choice.

Of course, if the channel 1 Ethernet is free, this is a viable option here too!

Regards,
George

Thanks for taking time for the detailed explanation, Geospark.