There are differences between index of modbus server register array and index of modbus client register array

[aigefjk]

When I test V5.5 library，I found there are differences between Modbus server register index and Modbus client register index.

Index of registers Modbus client class used is from 0 , while index of registers Modbus server class used is from 1.

e.g:

If you want to get value in holding register 0, you need pass index 0 to modbus client method but in modbus server method you must pass index 1 to the method.

public void WriteSingleRegister(int Addr, short Value)
{
MyServer.holdingRegisters.localArray[Addr + 1] = Value;
}

[Padanian]

For historical reasons, user reference numbers were expressed as decimal numbers with a starting offset of 1. However MODBUS uses the more natural software interpretation of an unsigned integer index starting at zero.

So a MODBUS message requesting the read of a register at offset 0 would return the value known to the application programmer as found in register 4:00001 (memory type 4 = output register, reference 00001).

[aigefjk]

For historical reasons, user reference numbers were expressed as decimal numbers with a starting offset of 1. However MODBUS uses the more natural software interpretation of an unsigned integer index starting at zero.

So a MODBUS message requesting the read of a register at offset 0 would return the value known to the application programmer as found in register 4:00001 (memory type 4 = output register, reference 00001).

---

Modbus client myClient.WriteSingleRegister(0, Value) update value in register 4:00001, but in modbus server localArray[1] presents 4:00001 , that not keep the same style.

[xsvold]

I can confirm this.

I can read and write using the same address on the server side. I can also due the same on the client side.

However, using another client, shows, that the data gets writen to different locations. (Client is +1)