When I try to create around 700 Modbus Registers in Ignition Gateway, I got internal error when I click on save button.
The limit is due to use of the address map. Don't use the address map, and you won't have any limit.
@pturmel is correct, 700 rows is too large for the address mapping feature in the gateway. Are you treating each row as a separate register or tag? If so, you are probably much better off manually creating the tags. Here's the relevant page in our documentation: Modbus - Manually Addressing
Alternatively, you can try grouping your tags so that each row in the address map represents more than one tag. I believe the form limitation is based only on the number of rows, not tags or registers.
Personally, I believe tags that are manually addressed are easier to understand. I would recommend that approach.
If you can share more about what you are trying to do, I would be happy to provide more specific examples.
