LabVIEW
I cannot read and write information using the Modbus API library and the serial port becomes unusable when the program is run.
Solved!
Is this still on the myRIO or have you moved to a normal PC? How did you connect the drive to your computer?
Since your device is configured to use station ID 127 (probably the same as communication port 0x007F) it could make a significant difference if you change the Modbus Unit ID on the LabVIEW side to 127 too. What's that about consistent naming you ask? Well ask the thousands of Modbus adopters worldwide. There's an "officious" Modbus standard as made by the original inventor Modicon and later passed to the Modbus Organization and maintained by them since. It specifies a lot of things but is pretty vague in many others. And it does simply call this element server address.
For RS-232 connections this element is usually not important as RS-232 is normally always a point to point connection, but in RS-422/485 networks it is very important. Some devices will ignore this address byte and answer irrespective of its value when connected through RS-232, others make no difference if they are connected over RS-422/485 or RS-232 and insist on correct addressing anyways.
That Modscan image is inconclusive at best!
You try to WRITE to Coil Address 01 in LabVIEW but READ 100 coils starting from address 1 and 2 in Modscan.
You try to READ 1 Holding Register from Address 00 in LabVIEW and none in Modscan.
The data you see in the Modscan screen is the serial data bytes SENT OUT to the device. Not what it returns. It most likely returns nothing as indicated by the Valid Slave Responses: 0.
Modbus is a general purpose bus. What the different register mean, what values they contain and which ones can be only read or also written is completely device specific.
As such you should of course refer to chapter 8 in this manual: https://downloadcenter.deltaww.com/downloadCenterCounter.aspx?DID=3948&DocPath=1&hl=en-US
Here the different registers are documented. As extra complication they seem to document the address of each register in byte offsets, whereas Modbus uses normally register offsets with each register being 2 bytes. And their registers are meant to be read and written as Holding Registers.
So in order to access any of these registers you probably want to use the Read or Write Holding Register function, apply an address that is half of what this manual describes for the relevant register and then specify the number of registers to read.
Try to do the same in the ModScan application (and set the Device ID there also to 127, Holding Register to access not Coils) and see if you get anything there that matches with what the LabVIEW VI returns. if you want to read a specific information you have to see what register that is then lookup its address in that manual, most likely divide it by 2 and enter that address in LabVIEW. Then see if you can make sense of that. Once you figured out the relevant details you can also try to change some registers but watch out that some of the registers are read only and will probably cause a Modbus exception if you try to write them.
