LabVIEW
I cannot read and write information using the Modbus API library and the serial port becomes unusable when the program is run.
Solved!
- Yes the LabVIEW Unit ID is synonymous to the drive's Station ID. Some other manufacturers call it Device ID, and the Modbus documentation calls it Server Address (might have been called Slave Address in the past but they did edit that document in 2020 to remove any mentioning of master and slave.
- The Start Address is the address of the first Modbus item (coil, register) you want to read. Note that LabVIEWs addressing convention is 0 based, the first register is address 0 and that it is for a 16 bit value, so byte addressing will use double the value to address the same value.
- Number of Inputs (or Outputs) is the number of registers to read starting from the Start Address.
- Register Value is the actual value a register contains. It is the value or values you receive from the Read Holding Register function or which you pass to the Write Holding Register function. Modbus registers are 16 bit integers.
Since your device seems to use byte addressing (P0-02 is at address 0x0004 and 0x0005) you would need to divide the first number of the two address values by two to get the LabVIEW Start Address to use for the Read Holding Register function, which here would be then 2.
Note that 0004H is a different way to write a hexadecimal address and is the same as 0x0004, and that also corresponds to 2 for the LabVIEW Address. If you want to read register P5-03, this would be at address 0506H and 0507H and since that is hexadecimal that would correspond to 1286 and 1287 decimal and translated to LabVIEW this would be 643 decimal.
Depending what display mode you set in LabVIEW for the control you can make it also use hexadecimal notation. It is only a display question the value underneath doesn't change, but the fact that this device uses byte addressing requires that you half the register value in the device documentation to get the actual Modbus address.
I think you got it the wrong way around.
It seems that the address shown in the documentation is actually the Modbus address. And each P value has two Modbus addresses reserved but does not always use it.
P0-09 is address 0012H and 0013H
It is documented to be a 32-bit value
Each Modbus address is only 16 bit however
So you need to read register 0x12 and 0x13 and then combine them to a 32 bit number.
P0-17 is address 0022H and 0023H.
But it is documented to only be a 16-bit value (and only have a range of 0-127)
This means you can simply read 0x0022 and only the lowest significant 7 bits are relevant of those 16-bits
Now you have here all hex numbers. You can set the LabVIEW control to also use hex format display by right clicking on it and in the menu, select Display Format. In the dialog that opens select Hexadecimal and close the dialog with OK. To help you see that this control is not set to display decimal numbers, right click again and select Visible Items->Radix. This will show a lowercase letter in front of the numbers, d means decimal, x means hexadecimal, o means octal and b means binary. When this Radix glyph is visible you always can also click on it and select the display mode there.
With the Start address set to show hexadecimal numbers you can directly enter the address as documented in the manual.
This is for registers documented as 32-bit numbers
For a 16 bit register you simply read the first element for the relevant address and throw away the next register as it is not used.
Why donāt you go through some of the LabVIEW tutorials linked on the main page of this forum? Hint: your problem has to do with array autoindexing
Not exactly. You now write 0 in the register immediately following the one you want to write. If it is only a16 bit register, the 0 value ends up being written into nirvana and probably has no effect but if it would be a 32-bit register you would overwrite the most significant 16 bit of that register with 0.
