What error do you get using 40001?
40001 is five digits isn’t it?
A lot of time the register is just “1”, drop the 4xxxx stuff - that is from old school PLCs that aren’t used anymore and the device makers can’t seem to get with the times on their documentation.
This device is indeed an older device. Then there is no way.
have you tried adding another 0? So the address is 400001?
@zhhpei to @Jakes point/question. Please help us help you by letting us know what you have tired and what errors you are seeing.
Thanks.
uggh - I forgot groov handles modbus address in a non-standard way.
If the device is saying to really use register 40001 - then this would be 440001 
according to that groov message. If the device is really wanting register 1, then it would be 400001 like Jakes suggested. If the device is listing the address (not register) then you need to add one to the values you try since it appears groov is wanting register locations since it starts with 1 (even though they call it address)
If only there was a published standard for everyone to follow: Modbus Specifications and Implementation Guides
