Modbus Addresses over 65535

Hello I have an application where I need to address modbus registers in the 400 000 to 449 651, but when creating address rows in my modbus device on the gateway, the register address is limited to 65 535. Is there a way to address modus registers over 65 536?

Are you sure the address syntax you’re being fed isn’t using the leading 4 to indicate it’s a Holding Register, and the addresses are in the 0 to 49651 range?

Anything above 65535 isn’t Modbus because it isn’t a 2 byte address any more.

These are the register addresses, the only thing I can think is that heaxadecimal addressing would allow for high register addresses.

Ignore the leading 4 and hope for the best.

Don’t use the address map until you’ve verified any addresses work. Create OPC tags manually, using the modbus addressing syntax described in the manual. Try unit/slave id 1 if the default 0 doesn’t work.


I think that it is a good chance that the addresses have got a prefix of 4 tacked on.

Number 4 meaning that this register is a Holding Register (2 bytes). 0-65535
400123 is holding register register 123.