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If you're receiving all 0's, then this may be an indication that your A and B wires are swapped. On some equipment A is + and B is -, but on others, it's reversed A is - and B is +. Try connecting A to B and B to A between the MAX485 and inverter.

Please re-read my response in post #28 carefully. It answers many of your questions and addresses your confusion. As I stated, the "Average phase Voltage U~" is at registers 30113 - 30114. This means you need to enter 113 for the Address and 2 for the Quantity (not 1). Also, as I mentioned...

Great, you've confirmed that the ABB inverter is responding correctly. This could be a case of a misleading error code taking us down the wrong path. It's possible the ModbusMaster library is returning this error as a catch-all due to some other issue. One guess is that the Arduino may be...

Are you using this Modbus library for the Arduino? https://github.com/4-20ma/ModbusMaster If so, the 0xE0 error code is explained here: https://4-20ma.io/ModbusMaster/group__constant.html#ga19521b4671bdc1ded03af72e2f3b958e The description of that error states, "The slave ID in the response...

Yes, it seems Modbus Poll is now successfully communicating with your MC 750. However, you have selected "03 Read Holding Registers (4x)" for the Function setting in your Read/Write Definition. You should select "04 Read Input Registers (3x)" since all of the registers documented in the MC 750's...

I just wanted to provide some clarification on this. You are seeing this because you connected using "Modbus UDP/IP". UDP is connectionless, meaning Modbus Poll does not establish a connection to the MC 750, but rather simply sends UDP packets to the MC 750's IP address. However, the MC 750...

As a separate suggestion, Iskra does provide their own software to connect to their products over Ethernet and seem to also support Modbus/TCP. The software is available here: https://www.iskra.eu/en/Iskra-Software/MiQen-Settings-Studio/ I recommend that you try using Iskra's own software to...

The Connection Failed error you're receiving means that your computer could not establish a TCP connection with the MC 750 on port 502. Therefore, changing the Slave ID will have no effect, because you are not even getting far enough for Modbus Poll to send a request to the MC 750. This may be...

There are a few Modbus specifications. All are listed here: https://modbus.org/specs.php Perhaps you were using the first link, MODBUS Protocol Specification, which is is the MODBUS APPLICATION PROTOCOL SPECIFICATION that mostly details the requests and responses. You want the MODBUS TCP/IP...

The response header is actually required to be identical to the request header (apart from the length). The use of each field is explained in the spec (see the Server column below)

Yes, the response needs to have the MBAP Header. This is implied in section 3.1.2 of the spec

I think you may be using the Modbus Poll software incorrectly. Your Communications Traffic from post #18 seems to show Modbus RTU packets because it includes a CRC at the end "C2 AD" (but for some reason without the address byte of 33 at the beginning). You may be trying to connect via serial...

The IP addresses of the MC 760 and your computer are very important! They must be on a compatible subnet. For example: Computer: IP Address: 192.168.1.12 Subnet Mask: 255.255.255.0 MC 760: IP Address: 192.168.1.13 Subnet Mask: 255.255.255.0 Please note that you may need to power cycle the MC...

Please try a Modbus/TCP client tool to confirm Modbus communications with the MC 760, such as ModScan, Simply Modbus, Modbus Poll, etc. After you have confirmed successful Modbus communications and confirmed the MC 760 can properly communicate Modbus with a third-party tool, then try getting...

I just looked at this again, and your request is invalid. You are sending the following bytes: 1234 0000 0004 21 03 75AE 0002 Which decodes into the following: Transaction Identifier: 4660 (0x1234) Protocol Identifier: 0 Length: 4 Incorrect, should be 6 Unit Identifier: 33 (0x21) This may need...

According to the manual, the MC 760 has two open ports: port 502 for Modbus/TCP and a user defined port. Therefore, there is no need to set any ports on the MC 760 because it always has port 502 open. From the manual: When port 502 is used a remote application(s) can access device...

What TCP port are you targeting? If you are trying to communicate Modbus/TCP to the device, you must use port 502. If you are using another port number, I think the power analyzer believes you are making a "terminal type of connection", which may be why it's simply echoing your requests. See...

The FC3 and FC4 issue you're seeing may be due to the way you have the VSE153 configured/programmed. In the manual, it shows that registers 30001 - 30015 map to %IW0 - %IW14 and 40001 - 40015 map to %QW0 - %QW14. The %IWx and %QWx addresses are internal memory locations in the VSE153 for input...

Section 8.1 in the VSE153 manual you linked shows the maximum length for writes and reads as 123 and 125, respectively, which is the maximum limit for all Modbus RTU devices. Therefore, I do not believe this is the cause of your issue. However, according to the VSE153 manual register 39000 and...

It doesn't seem like you're doing anything wrong, but rather possibly running into a limitation of the VES device's Modbus implementation. Can you share the Modbus documentation for the VES device? Maybe there is a mention of such limitations. There are two things that I can think of that could...