Modbus Read/Write registers

[PLCUser007]

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.

 

In here Reading address 800 via modbus looks to be ok

 

 

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'?

 

 

 

 

[PLCUser007]

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?

 

[panic mode]

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

 

[panic mode]

check this out

http://www.tri-plc.com/appnotes/modbus-map.pdf