Multiple protocols on RS-485 Network?

Is it possible for Modbus RTU and DH-485 to reside on the same physical network?

I have a couple temperature controllers that can act as Modbus slaves. Running a separate cable to them won't be fun. However, there's a DH-485 cable right beside them that I could connect to.

Has anyone ever tried this?

rguimond said:

Is it possible for Modbus RTU and DH-485 to reside on the same physical network?

I have a couple temperature controllers that can act as Modbus slaves. Running a separate cable to them won't be fun. However, there's a DH-485 cable right beside them that I could connect to.

Has anyone ever tried this?

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My gut reaction would be no. However, exactly which PLC are we talking about here? If you do not need constant updates of both types of devices, and the Comm Port can be re-configured on the fly, it might be possible. Having said that, are the voltage levels compatible between the two protocols? Would it be worth the risk of damaging one of the devices, or causing confusion with the device not actually being communicated to seeing garbage data?

Stu.....

See, those are the types of things I'm wondering about. If the answer is "no", that's fine - I'll run another cable.

Hardware as follows:

3 x SLC 5/03 on DH-485 network
1 x C-More HMI reading a total of six tags (2 from each SLC 5/03)
1 x SLC 5/05 set up as DH-485 pass-through (1761-NET-AIC module on port "0" of 5/05 and DH-485 network)

I would recommend a DH-485 to Modbus protocol converter, making the temp. controller(s) a DH-485 slave on the network. I'd normally recommend a Red Lion Data Station for this, but I don't think they have DH-485 slave protocol.

If both protocols are master/slave and the same device is acting as master for both DH485 and RTU, then it could work. It would be up to you to program the master so that it only talks one protocol at a time. I'm not familiar enough with the DH485 protocol to offer much more than that.

Is it possible for Modbus RTU and DH-485 to reside on the same physical network?

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It's a reasonable question, but the answer is "definitely not".

There is no way for the token-passing mechanism of DH-485 and the Master/Slave mechanism of Modbus RTU to co-exist without interference.

If you have an IP network running nearby, there are Modbus/EtherNetIP interface boxes available (I like RTA's device) that you could access via MSG from the SLC-5/05. Remember also that FRN11 for SLC controllers includes Modbus RTU Master on the serial port.

I like the MLX 1100 you can use them as a bridge betweeen the Ethernet and Modbus RTU.

I like the Real Time Automation stuff to. It will bridge just about anything you want. Very quick setup.