Reading Modbus w/ PLC

FNC

Member
Join Date
May 2010
Location
NJ
Posts
84
I am using a PLC to read some Modbus addresses from a Yokogawa GM10 data recorder. The addresses are 302001-302010, and also 415001-415010?

I thought addresses had to be no more than 65,535.

Is address 302001 the same as 2001???

What about address 415001?

Thanks.

FNC
 
Some software uses 400000 insteaf of 40000 (they all have an Extra 0.

I am not sure why exactly, im hoping someone else can enlighten me on this,

But for 302001, it would be 32001, etc.

Im just not sure on the 415001.
It is very possible that it talks enron modbus, and Function code 3 (read analog inputs), register 2001 and function code 4 (read holding registers), register 15001...
 
telling more about the plc and soft used could help because it would be different from one to another.
Some will decide of the first number by using a function code and then you just type the other numbers.
 
Modbus addressing is notoriously confusing to novices because the prefix digit describes the data table type, not the "10 thousands place" offset.

0 Discrete Output Coils
1 Discrete Input Contacts
2 not used
3 Analog Input Registers
4 Analog Output (Holding) Registers

Most users will number the first Holding register as "40001", even though the Function Code to read it is 0x03 and the Offset is 0x00.

Some vendors add another zero, some consider the first register to be 0 instead of 1... it gets weird.

Page 332 of this user manual gives some interesting information:

https://web-material3.yokogawa.com/IM04L55B01-01EN_012.pdf


The data from "sub unit 2" is considered Yokogawa "Channel 2001 data", which is represented as Modbus register 315001.


My quick reading of that manual suggests that the same data can be read as a "Analog Input" or as an "Analog Output / Holding" register, so as a 3000x address or as a 4000x address.
 

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