Sign in to follow this  
Followers 0
PLCUser007

Modbus Read/Write registers

4 posts in this topic

I'm trying to Read/Write registers via modbus RTU. I can Read values but can not set values.

 

Here is a screenshot of my setup. in this test setup values are set by hand.

2020-03-30_104322.thumb.png.3b668518e543

 

In here Reading address 800 via modbus looks to be ok

2020-03-30_104504.thumb.png.ad84ff31ceb8

 

 

And here trying to change the state of the values to 0.  the bus monitor says written correctly, but when read the values back they are still '00000000000000111'?

2020-03-30_104648.thumb.png.f87c0a7bc92a

 

 

 

 

Share this post


Link to post
Share on other sites

the modbus address are not the same as plc memory address. Does anyone have an IO map of modbus address or knows how to calculate the memory address?

 

Share this post


Link to post
Share on other sites

if the monitor says it is writen correctly, it is writen correctly.

in Modbus, inputs, coils, holding registers etc are diffreent memory blocks. your first example is reading input block. your second example is writing to a register but you are still monitoring the input block. 

not sure how they are mapped in Omron but check D or H areas for example

and check if they are already used, maybe the location is immediately overwriten by some running code

 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0