the last line says no space left so the above command should reveal something, what size micro SD card are you using? Did you write the emonSD image to the card yourself or buy it from the shop? If the former, did you use emonExpand to expand the filesystem and partitions to fill the card?
I now have the interface installed and sort of working.
If I set the register to 40001 I get “Connection failed on read of register: 40001” the same for 30001. but if I change it to 1 I get the correct data back for register 30001
From the manual I have
function code 0X04
Register 0x0001
Data Format Int16
length 1
If I use Modbus master I am able to see the correct values for 0x04 and 0x03 with registers 0-125