Link Wizard

[Henryp]

The Directsoft 5 link wizard has the ability to auto detect a Directnet or K-Sequence device, it can auto select various baud rates and supports a user selectable device id.  As a troubleshooting tool would it be possible to add the Modbus protocol to the existing link wizard or break the link wizard out into a small standalone test tool?

[franji1]

The Link Wizard itself would not be the tool, but a similar functioning dialog that could iterate a set of common baud rates on a predefined COMx serial port and possibly a predefined Unit ID - I think that is what you are wanting?

Texas Instruments developed a utility for the Koyo PLC's that mapped out your 485 network of TI-305 and TI-405 PLCs.  Sounds like you want something similar, except for Modbus?

[Henryp]

Yes, a utility like the link wizard but for Modbus. When trying to do a Modbus serial connection to an Automation Direct PLC it can be a challenging task. The 450, 250 and Do More CPUs all have different communication ports with different pin-outs. The use of an Isonet or Isoconn converter adds another device to configure.  The end result is that when Modbus communications don’t work, a lot of time can be wasted trying to figure out the problem. 

[franji1]

This utility would actually need to be quite complex based off whether the PLC was the Master or the Slave, and whether you are diagnosing with or without isonet/isoconn (PCs typically have only RS-232 ports).

This could involve multiple cables (i.e. sticking a PC on a multi-drop 485 network).

Is the PLC a Modbus/RTU Master vs. a Modbus/RTU Slave - there would be 2 completely different tools based on the two different network setups.

If the PLC is the Master, then an "Aux Function" command would have to be written in the PLC firmware and sent by the programming software for the PLC to run the "auto-baud" sequencing, then report back to programming software the results.

If the PLC is the Slave, then you could isolate the PLC and have a point-to-point RS-232 connection (?), but that doesn't help you figure out why your master can't talk to it, other than report the baud rate and unit id based on the 232 point-to-point.

Please describe in detail your network setup (i.e. what is the Modbus Master and what are all of the Modbus Slaves).

I think what you actually need is a multi-drop 485 packet sniffer PC utility, along with special cabling that can "tap in" to your 485 network.  I've rigged these up myself where the RX goes to COM1 RX and the TX goes to COM2 RX on my PC, and used a shareware that shows the traffic on the two com ports.  Is this what you need?

For Ethernet, there is a utility called WireShark that works GREAT for this kind of debugging (we use it with our customers all the time).  You probably want SerialWireShark in your Master PLC or as a "sniffer" running on a PC?

[Henryp]

The links are always point to point, a converter is only used to extend beyond 50 feet. We use three types of links, AD PLC to AD PLC, AD PLC to VFD and AD PLC to Modbus power monitors. The last 260 to GS3 was very challenging, for communications to work I must have the ports setup the same, the cables made properly, I have to figure out the Modbus to AD addressing and make sure (as in the case of the GS3) that I don't read too many addresses.  The GS3 register are not concurrent if six registers exist and I read seven the GS3 will report bad data on the display  and the ladder will get  a communication  error but nowhere is the actual Modbus exception displayed.

[franji1]

The links are always point to point, a converter is only used to extend beyond 50 feet. We use three types of links, AD PLC to AD PLC, AD PLC to VFD and AD PLC to Modbus power monitors. The last 260 to GS3 was very challenging, for communications to work I must have the ports setup the same, the cables made properly, I have to figure out the Modbus to AD addressing and make sure (as in the case of the GS3) that I don't read too many addresses.  The GS3 register are not concurrent if six registers exist and I read seven the GS3 will report bad data on the display  and the ladder will get  a communication  error but nowhere is the actual Modbus exception displayed.

So it sounds like you need the "link wizard" functionality in the PLC, not in the PC?  So the PLC would cycle through various baud rates (but not Unit ID since they are all point-to-point, so can be assumed to be 1 or some other fixed number?).  Sadly, this would require new functionality in the PLC, not just in DirectSOFT.  We recommend you make your request to Automation Direct on their website.

However, Host can look at providing this feature with a Do-more CPU and Designer in a future version.