User is getting -1 when reading an externa numeric register. The user may notice that any changes to this register will not save
ION 7550 and ION7500 RTU
The ION 75xx RTU units do not come with predefined framework on the meters. If a module does not exist on the framework, modbus requests will return -1.
Use ION Setup or ION Designer to create external numeric modules and unlock the registers. Once the module has been created the register will read 0 instead of -1.