Modbus implementation

Your meter's Modbus implementation includes exception codes, invalid register responses, fixed and configurable register maps, and security.

Modbus exception codes

Code Name Description


Illegal function

The requested command is invalid.


Illegal address

This code indicates one of the following:

  • The requested address is invalid for that function.

  • The requested address is not within the valid register range for this device.

  • The requested address is protected by device security.


Illegal value

This code indicates one of the following:

  • The requested value is not allowed for that register in the device.

  • The requested register is part of a multi-word value.

Modbus invalid read registers responses

Invalid type Read response

Unmapped (unused)1 register


Reserved1 register responses by type

Signed integer 16-bit


Unsigned integer 16-bit


Signed integer 32-bits


Unsigned integer 32-bits


Signed integer 64-bits




(NaN = Not a number)

1 IRIG-B can only be connected to one of the digital inputs located on the meter base, not an option module. Unmapped (unused) registers are registers that will never be used by the meter, and therefore have no defined format. Reserved registers have a defined format and are intended for use by the meter, its options or its variants.

Modbus invalid write registers response

If the meter receives a write command to a Modbus register address that does not have a register mapped, the meter will not respond. No data is written or stored, and the meter will not send back a rejection to the request.

If the meter receives a write command to a read-only Modbus register address, exception code 3 (illegal value) is returned.

Fixed and configurable Modbus map

Your device has a fixed (static) register map for meter data and a flexible, user-configured register map.

Modbus security

Your meter’s onboard security options include Modbus-specific settings. These security settings may need to be configured in order to write Modbus data to the meter.

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