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MangoAutomation / modbus4j

A high-performance and ease-of-use implementation of the Modbus protocol written in Java. Supports ASCII, RTU, TCP, and UDP transports as slave or master, automatic request partitioning and response data type parsing.
GNU General Public License v3.0
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Floating Point Number is Not Accurate in modbusTcp #35

Closed JunshiJia closed 4 years ago

JunshiJia commented 4 years ago

Hello, recently I use lots of the read and write FOUR_BYTE_FLOAT function(batchRead) in your MODBUS TCP module, I found the number is not accurate(maybe my own problem). More specific, the float numbers generally have an error of 0.5%, which is not normal for floating point numbers.

I am guessing, is it possible that the 3rd and 4th bytes are flipped that causes this problem?

Does anyone else has this problem?

JunshiJia commented 4 years ago

So I did more test. I use your module to Write 30000 float point number on a slave address for 4bytes float, and use another java module(called easy modbus) to read this addres, i got 299584.0. This should be a bug, right?

Wrote 3.0E7, read 2.992128E7.

ghost commented 4 years ago

@JunshiJia ，this is not modbus4j bug, may be occured when you use the value,you can use the java BigDecimal instead of the double or flout,it have the accuracy problem.

JunshiJia commented 4 years ago

@minghu Actually I think you are right. I did more tests found my bug. I am truly an amateur got to admit that.